CVE-2026-4873

A vulnerability exists where a connection requiring TLS incorrectly reuses an existing unencrypted connection from the same connection pool. If an initial transfer is made in clear-text (via IMAP, SMTP, or POP3), a subsequent request to that same host bypasses the TLS requirement and instead transmit data unencrypted.

A vulnerability exists where a connection requiring TLS incorrectly reuses an existing unencrypted connection from the same connection pool. If an initial transfer is made in clear-text (via IMAP, SMTP, or POP3), a subsequent request to that same host bypasses the TLS requirement and instead transmit data unencrypted.

A vulnerability exists where a connection requiring TLS incorrectly reuses an existing unencrypted connection from the same connection pool. If an initial transfer is made in clear-text (via IMAP, SMTP, or POP3), a subsequent request to that same host bypasses the TLS requirement and instead transmit data unencrypted.

cURL is a computer software project providing a library (libcurl) and command-line tool (curl) for transferring data using various protocols.

Security Fix(es):

A vulnerability exists where a connection requiring TLS incorrectly reuses an existing unencrypted connection from the same connection pool. If an initial transfer is made in clear-text (via IMAP, SMTP, or POP3), a subsequent request to that same host bypasses the TLS requirement and instead transmit data unencrypted.(CVE-2026-4873)

libcurl might in some circumstances reuse the wrong connection when asked to do an authenticated HTTP(S) request after a Negotiate-authenticated one, when both use the same host.

libcurl features a pool of recent connections so that subsequent requests can reuse an existing connection to avoid overhead.

When reusing a connection a range of criteria must be met. Due to a logical error in the code, a request that was issued by an application could wrongfully reuse an existing connection to the same server that was authenticated using different credentials.

An application that first uses Negotiate authentication to a server with user1:password1 and then does another operation to the same server asking for any authentication method but for user2:password2 (while the previous connection is still alive) - the second request gets confused and wrongly reuses the same connection and sends the new request over that connection thinking it uses a mix of user1's and user2's credentials when it is in fact still using the connection authenticated for user1...(CVE-2026-5545)

libcurl might in some circumstances reuse the wrong connection for SMB(S) transfers.

libcurl features a pool of recent connections so that subsequent requests can reuse an existing connection to avoid overhead.

When reusing a connection a range of criteria must be met. Due to a logical error in the code, a network transfer operation that was requested by an application could wrongfully reuse an existing SMB connection to the same server that was using a different 'share' than the new subsequent transfer should.

This could in unlucky situations lead to the download of the wrong file or the upload of a file to the wrong place. When this happens, the same credentials are used and the server name is the same.(CVE-2026-5773)

curl might erroneously pass on credentials for a first proxy to a second proxy.

This can happen when the following conditions are true:

1. curl is setup to use specific different proxies for different URL schemes
2. the first proxy needs credentials
3. the second proxy uses no credentials
4. while using the first proxy (using say http://), curl is asked to follow a redirect to a URL using another scheme (say https://), accessed using a second, different, proxy(CVE-2026-6253)

Using libcurl, when a custom Host: header is first set for an HTTP request and a second request is subsequently done using the same easy handle but without the custom Host: header set, the second request would use stale information and pass on cookies meant for the first host in the second request. Leak them.(CVE-2026-6276)

When asked to both use a .netrc file for credentials and to follow HTTP redirects, libcurl could leak the password used for the first host to the followed-to host under certain circumstances.(CVE-2026-6429)

Successfully using libcurl to do a transfer over a specific HTTP proxy (proxyA) with Digest authentication and then changing the proxy host to a second one (proxyB) for a second transfer, reusing the same handle, makes libcurl wrongly pass on the Proxy-Authorization: header field meant for proxyA, to proxyB.(CVE-2026-7168)

cURL is a computer software project providing a library (libcurl) and command-line tool (curl) for transferring data using various protocols.

Security Fix(es):

A vulnerability exists where a connection requiring TLS incorrectly reuses an existing unencrypted connection from the same connection pool. If an initial transfer is made in clear-text (via IMAP, SMTP, or POP3), a subsequent request to that same host bypasses the TLS requirement and instead transmit data unencrypted.(CVE-2026-4873)

libcurl might in some circumstances reuse the wrong connection when asked to do an authenticated HTTP(S) request after a Negotiate-authenticated one, when both use the same host.

libcurl features a pool of recent connections so that subsequent requests can reuse an existing connection to avoid overhead.

When reusing a connection a range of criteria must be met. Due to a logical error in the code, a request that was issued by an application could wrongfully reuse an existing connection to the same server that was authenticated using different credentials.

An application that first uses Negotiate authentication to a server with user1:password1 and then does another operation to the same server asking for any authentication method but for user2:password2 (while the previous connection is still alive) - the second request gets confused and wrongly reuses the same connection and sends the new request over that connection thinking it uses a mix of user1's and user2's credentials when it is in fact still using the connection authenticated for user1...(CVE-2026-5545)

libcurl might in some circumstances reuse the wrong connection for SMB(S) transfers.

libcurl features a pool of recent connections so that subsequent requests can reuse an existing connection to avoid overhead.

When reusing a connection a range of criteria must be met. Due to a logical error in the code, a network transfer operation that was requested by an application could wrongfully reuse an existing SMB connection to the same server that was using a different 'share' than the new subsequent transfer should.

This could in unlucky situations lead to the download of the wrong file or the upload of a file to the wrong place. When this happens, the same credentials are used and the server name is the same.(CVE-2026-5773)

curl might erroneously pass on credentials for a first proxy to a second proxy.

This can happen when the following conditions are true:

1. curl is setup to use specific different proxies for different URL schemes
2. the first proxy needs credentials
3. the second proxy uses no credentials
4. while using the first proxy (using say http://), curl is asked to follow a redirect to a URL using another scheme (say https://), accessed using a second, different, proxy(CVE-2026-6253)

Using libcurl, when a custom Host: header is first set for an HTTP request and a second request is subsequently done using the same easy handle but without the custom Host: header set, the second request would use stale information and pass on cookies meant for the first host in the second request. Leak them.(CVE-2026-6276)

When asked to both use a .netrc file for credentials and to follow HTTP redirects, libcurl could leak the password used for the first host to the followed-to host under certain circumstances.(CVE-2026-6429)

Successfully using libcurl to do a transfer over a specific HTTP proxy (proxyA) with Digest authentication and then changing the proxy host to a second one (proxyB) for a second transfer, reusing the same handle, makes libcurl wrongly pass on the Proxy-Authorization: header field meant for proxyA, to proxyB.(CVE-2026-7168)

cURL is a computer software project providing a library (libcurl) and command-line tool (curl) for transferring data using various protocols.

Security Fix(es):

A vulnerability exists where a connection requiring TLS incorrectly reuses an existing unencrypted connection from the same connection pool. If an initial transfer is made in clear-text (via IMAP, SMTP, or POP3), a subsequent request to that same host bypasses the TLS requirement and instead transmit data unencrypted.(CVE-2026-4873)

libcurl might in some circumstances reuse the wrong connection when asked to do an authenticated HTTP(S) request after a Negotiate-authenticated one, when both use the same host.

libcurl features a pool of recent connections so that subsequent requests can reuse an existing connection to avoid overhead.

When reusing a connection a range of criteria must be met. Due to a logical error in the code, a request that was issued by an application could wrongfully reuse an existing connection to the same server that was authenticated using different credentials.

An application that first uses Negotiate authentication to a server with user1:password1 and then does another operation to the same server asking for any authentication method but for user2:password2 (while the previous connection is still alive) - the second request gets confused and wrongly reuses the same connection and sends the new request over that connection thinking it uses a mix of user1's and user2's credentials when it is in fact still using the connection authenticated for user1...(CVE-2026-5545)

libcurl might in some circumstances reuse the wrong connection for SMB(S) transfers.

libcurl features a pool of recent connections so that subsequent requests can reuse an existing connection to avoid overhead.

When reusing a connection a range of criteria must be met. Due to a logical error in the code, a network transfer operation that was requested by an application could wrongfully reuse an existing SMB connection to the same server that was using a different 'share' than the new subsequent transfer should.

This could in unlucky situations lead to the download of the wrong file or the upload of a file to the wrong place. When this happens, the same credentials are used and the server name is the same.(CVE-2026-5773)

curl might erroneously pass on credentials for a first proxy to a second proxy.

This can happen when the following conditions are true:

1. curl is setup to use specific different proxies for different URL schemes
2. the first proxy needs credentials
3. the second proxy uses no credentials
4. while using the first proxy (using say http://), curl is asked to follow a redirect to a URL using another scheme (say https://), accessed using a second, different, proxy(CVE-2026-6253)

Using libcurl, when a custom Host: header is first set for an HTTP request and a second request is subsequently done using the same easy handle but without the custom Host: header set, the second request would use stale information and pass on cookies meant for the first host in the second request. Leak them.(CVE-2026-6276)

When asked to both use a .netrc file for credentials and to follow HTTP redirects, libcurl could leak the password used for the first host to the followed-to host under certain circumstances.(CVE-2026-6429)

Successfully using libcurl to do a transfer over a specific HTTP proxy (proxyA) with Digest authentication and then changing the proxy host to a second one (proxyB) for a second transfer, reusing the same handle, makes libcurl wrongly pass on the Proxy-Authorization: header field meant for proxyA, to proxyB.(CVE-2026-7168)

cURL is a computer software project providing a library (libcurl) and command-line tool (curl) for transferring data using various protocols.

Security Fix(es):

A vulnerability exists where a connection requiring TLS incorrectly reuses an existing unencrypted connection from the same connection pool. If an initial transfer is made in clear-text (via IMAP, SMTP, or POP3), a subsequent request to that same host bypasses the TLS requirement and instead transmit data unencrypted.(CVE-2026-4873)

libcurl might in some circumstances reuse the wrong connection when asked to do an authenticated HTTP(S) request after a Negotiate-authenticated one, when both use the same host.

libcurl features a pool of recent connections so that subsequent requests can reuse an existing connection to avoid overhead.

When reusing a connection a range of criteria must be met. Due to a logical error in the code, a request that was issued by an application could wrongfully reuse an existing connection to the same server that was authenticated using different credentials.

An application that first uses Negotiate authentication to a server with user1:password1 and then does another operation to the same server asking for any authentication method but for user2:password2 (while the previous connection is still alive) - the second request gets confused and wrongly reuses the same connection and sends the new request over that connection thinking it uses a mix of user1's and user2's credentials when it is in fact still using the connection authenticated for user1...(CVE-2026-5545)

libcurl might in some circumstances reuse the wrong connection for SMB(S) transfers.

libcurl features a pool of recent connections so that subsequent requests can reuse an existing connection to avoid overhead.

When reusing a connection a range of criteria must be met. Due to a logical error in the code, a network transfer operation that was requested by an application could wrongfully reuse an existing SMB connection to the same server that was using a different 'share' than the new subsequent transfer should.

This could in unlucky situations lead to the download of the wrong file or the upload of a file to the wrong place. When this happens, the same credentials are used and the server name is the same.(CVE-2026-5773)

curl might erroneously pass on credentials for a first proxy to a second proxy.

This can happen when the following conditions are true:

1. curl is setup to use specific different proxies for different URL schemes
2. the first proxy needs credentials
3. the second proxy uses no credentials
4. while using the first proxy (using say http://), curl is asked to follow a redirect to a URL using another scheme (say https://), accessed using a second, different, proxy(CVE-2026-6253)

Using libcurl, when a custom Host: header is first set for an HTTP request and a second request is subsequently done using the same easy handle but without the custom Host: header set, the second request would use stale information and pass on cookies meant for the first host in the second request. Leak them.(CVE-2026-6276)

When asked to both use a .netrc file for credentials and to follow HTTP redirects, libcurl could leak the password used for the first host to the followed-to host under certain circumstances.(CVE-2026-6429)

Successfully using libcurl to do a transfer over a specific HTTP proxy (proxyA) with Digest authentication and then changing the proxy host to a second one (proxyB) for a second transfer, reusing the same handle, makes libcurl wrongly pass on the Proxy-Authorization: header field meant for proxyA, to proxyB.(CVE-2026-7168)

cURL is a computer software project providing a library (libcurl) and command-line tool (curl) for transferring data using various protocols.

Security Fix(es):

A vulnerability exists where a connection requiring TLS incorrectly reuses an existing unencrypted connection from the same connection pool. If an initial transfer is made in clear-text (via IMAP, SMTP, or POP3), a subsequent request to that same host bypasses the TLS requirement and instead transmit data unencrypted.(CVE-2026-4873)

libcurl might in some circumstances reuse the wrong connection when asked to do an authenticated HTTP(S) request after a Negotiate-authenticated one, when both use the same host.

libcurl features a pool of recent connections so that subsequent requests can reuse an existing connection to avoid overhead.

When reusing a connection a range of criteria must be met. Due to a logical error in the code, a request that was issued by an application could wrongfully reuse an existing connection to the same server that was authenticated using different credentials.

An application that first uses Negotiate authentication to a server with user1:password1 and then does another operation to the same server asking for any authentication method but for user2:password2 (while the previous connection is still alive) - the second request gets confused and wrongly reuses the same connection and sends the new request over that connection thinking it uses a mix of user1's and user2's credentials when it is in fact still using the connection authenticated for user1...(CVE-2026-5545)

libcurl might in some circumstances reuse the wrong connection for SMB(S) transfers.

libcurl features a pool of recent connections so that subsequent requests can reuse an existing connection to avoid overhead.

When reusing a connection a range of criteria must be met. Due to a logical error in the code, a network transfer operation that was requested by an application could wrongfully reuse an existing SMB connection to the same server that was using a different 'share' than the new subsequent transfer should.

This could in unlucky situations lead to the download of the wrong file or the upload of a file to the wrong place. When this happens, the same credentials are used and the server name is the same.(CVE-2026-5773)

curl might erroneously pass on credentials for a first proxy to a second proxy.

This can happen when the following conditions are true:

1. curl is setup to use specific different proxies for different URL schemes
2. the first proxy needs credentials
3. the second proxy uses no credentials
4. while using the first proxy (using say http://), curl is asked to follow a redirect to a URL using another scheme (say https://), accessed using a second, different, proxy(CVE-2026-6253)

Using libcurl, when a custom Host: header is first set for an HTTP request and a second request is subsequently done using the same easy handle but without the custom Host: header set, the second request would use stale information and pass on cookies meant for the first host in the second request. Leak them.(CVE-2026-6276)

When asked to both use a .netrc file for credentials and to follow HTTP redirects, libcurl could leak the password used for the first host to the followed-to host under certain circumstances.(CVE-2026-6429)

Successfully using libcurl to do a transfer over a specific HTTP proxy (proxyA) with Digest authentication and then changing the proxy host to a second one (proxyB) for a second transfer, reusing the same handle, makes libcurl wrongly pass on the Proxy-Authorization: header field meant for proxyA, to proxyB.(CVE-2026-7168)

Root has patched CVE-2026-4873 in the curl package for Root:Debian:11. Multiple fixed versions available.

Root has patched CVE-2026-4873 in the curl package for Root:Debian:12. Multiple fixed versions available.

Root has patched CVE-2026-4873 in the rootio-curl package for Root:Debian:13. Multiple fixed versions available.

A vulnerability exists where a connection requiring TLS incorrectly reuses an existing unencrypted connection from the same connection pool. If an initial transfer is made in clear-text (via IMAP, SMTP, or POP3), a subsequent request to that same host bypasses the TLS requirement and instead transmit data unencrypted.

A vulnerability exists where a connection requiring TLS incorrectly reuses an existing unencrypted connection from the same connection pool. If an initial transfer is made in clear-text (via IMAP, SMTP, or POP3), a subsequent request to that same host bypasses the TLS requirement and instead transmit data unencrypted.

A vulnerability exists where a connection requiring TLS incorrectly reuses an existing unencrypted connection from the same connection pool. If an initial transfer is made in clear-text (via IMAP, SMTP, or POP3), a subsequent request to that same host bypasses the TLS requirement and instead transmit data unencrypted.

• CVE-2026-4873: do not reuse a clear-text STARTTLS connection when the new transfer requires TLS, so an IMAP, SMTP or POP3 request that mandates TLS is not sent over an unencrypted connection
• CVE-2026-6253: restore the proxy credentials set via options on every redirect so credentials belonging to the first proxy are not disclosed to a second, different proxy
• CVE-2026-6429: drop credentials that were not set through CURLOPT_USERNAME on redirect so a netrc password established for the first host is not sent to the redirect target over a reused connection or proxy
• CVE-2026-8924: trim trailing dots from the request and cookie domains before the public suffix list check so a trailing-dot domain cannot set a super cookie scoped to an unrelated site

• CVE-2026-4873: do not reuse a clear-text STARTTLS connection when the new transfer requires TLS, so an IMAP, SMTP or POP3 request that mandates TLS is not sent over an unencrypted connection
• CVE-2026-6253: restore the proxy credentials set via options on every redirect so credentials belonging to the first proxy are not disclosed to a second, different proxy
• CVE-2026-6429: drop credentials that were not set through CURLOPT_USERNAME on redirect so a netrc password established for the first host is not sent to the redirect target over a reused connection or proxy
• CVE-2026-8924: trim trailing dots from the request and cookie domains before the public suffix list check so a trailing-dot domain cannot set a super cookie scoped to an unrelated site

A vulnerability exists where a connection requiring TLS incorrectly reuses an existing unencrypted connection from the same connection pool. If an initial transfer is made in clear-text (via IMAP, SMTP, or POP3), a subsequent request to that same host bypasses the TLS requirement and instead transmit data unencrypted.

These are all security issues fixed in the curl-8.20.0-1.1 package on the GA media of openSUSE Tumbleweed.

This update for curl fixes the following issues:

• CVE-2026-4873: connection reuse ignores TLS requirement (bsc#1262631).
• CVE-2026-5545: wrong reuse of HTTP Negotiate connection (bsc#1262632).
• CVE-2026-6253: proxy credentials leak over redirect-to proxy (bsc#1262635).
• CVE-2026-6276: stale custom cookie host causes cookie leak (bsc#1262636).
• CVE-2026-6429: netrc credential leak with reused proxy connection (bsc#1262638).

This update for curl fixes the following issues:

Security issues fixed:

• CVE-2026-4873: connection reuse ignores TLS requirement (bsc#1262631).
• CVE-2026-5545: wrong reuse of HTTP Negotiate connection (bsc#1262632).
• CVE-2026-6253: proxy credentials leak over redirect-to proxy (bsc#1262635).
• CVE-2026-6276: stale custom cookie host causes cookie leak (bsc#1262636).
• CVE-2026-6429: netrc credential leak with reused proxy connection (bsc#1262638).

Other updates and bugfixes:

• sws: prevent 'connection monitor' to say disconnect twice (bsc#1259362).

This update for curl fixes the following issues:

Security issues fixed:

• CVE-2026-4873: connection reuse ignores TLS requirement (bsc#1262631).
• CVE-2026-5545: wrong reuse of HTTP Negotiate connection (bsc#1262632).
• CVE-2026-6253: proxy credentials leak over redirect-to proxy (bsc#1262635).
• CVE-2026-6276: stale custom cookie host causes cookie leak (bsc#1262636).
• CVE-2026-6429: netrc credential leak with reused proxy connection (bsc#1262638).

Other updates and bugfixes:

• sws: prevent 'connection monitor' to say disconnect twice (bsc#1259362).

This update for curl fixes the following issues:

Security issues fixed:

• CVE-2026-4873: connection reuse ignores TLS requirement (bsc#1262631).
• CVE-2026-5545: wrong reuse of HTTP Negotiate connection (bsc#1262632).
• CVE-2026-6253: proxy credentials leak over redirect-to proxy (bsc#1262635).
• CVE-2026-6276: stale custom cookie host causes cookie leak (bsc#1262636).
• CVE-2026-6429: netrc credential leak with reused proxy connection (bsc#1262638).

Other updates and bugfixes:

• sws: prevent "connection monitor" to say disconnect twice (bsc#1259362).

This update for curl fixes the following issues:

• CVE-2026-4873: connection reuse ignores TLS requirement (bsc#1262631).
• CVE-2026-5545: wrong reuse of HTTP Negotiate connection (bsc#1262632).
• CVE-2026-6253: proxy credentials leak over redirect-to proxy (bsc#1262635).
• CVE-2026-6276: stale custom cookie host causes cookie leak (bsc#1262636).
• CVE-2026-6429: netrc credential leak with reused proxy connection (bsc#1262638).

This update for curl fixes the following issues:

• CVE-2026-4873: connection reuse ignores TLS requirement (bsc#1262631).
• CVE-2026-5545: wrong reuse of HTTP Negotiate connection (bsc#1262632).
• CVE-2026-6253: proxy credentials leak over redirect-to proxy (bsc#1262635).
• CVE-2026-6276: stale custom cookie host causes cookie leak (bsc#1262636).
• CVE-2026-6429: netrc credential leak with reused proxy connection (bsc#1262638).

This update for curl fixes the following issues

• CVE-2026-4873: connection reuse ignores TLS requirement (bsc#1262631).
• CVE-2026-5545: wrong reuse of HTTP Negotiate connection (bsc#1262632).
• CVE-2026-5773: wrong reuse of SMB connection (bsc#1262633).
• CVE-2026-6253: proxy credentials leak over redirect-to proxy (bsc#1262635).
• CVE-2026-6276: stale custom cookie host causes cookie leak (bsc#1262636).
• CVE-2026-6429: netrc credential leak with reused proxy connection (bsc#1262638).

This update for curl fixes the following issues

• CVE-2026-4873: connection reuse ignores TLS requirement (bsc#1262631).
• CVE-2026-8286: wrong STARTTLS connection reuse (bsc#1268402).
• CVE-2026-8458: wrong reuse for different services (bsc#1268407).
• CVE-2026-8924: traling dot domain super cookie (bsc#1268409).
• CVE-2026-8927: env-set cross-proxy Digest auth state leak (bsc#1268413).
• CVE-2026-9079: stale proxy password leak (bsc#1268415).
• CVE-2026-9080: UAF after pause in socket callback (bsc#1268416).
• CVE-2026-9545: exposing HTTP/3 early data (bsc#1268417).
• CVE-2026-9547: SSH improper host validation (bsc#1268420).
• CVE-2026-10536: HTTP/2 stream-dependency tree UAF (bsc#1268422).
• CVE-2026-12064: proto-default skips SSH verification (bsc#1268427).

It was discovered that curl incorrectly reused non-TLS connections when TLS was required in some STARTTLS configurations. A remote attacker could possibly use this issue to obtain sensitive information. (CVE-2026-4873)

It was discovered that curl incorrectly reused certain HTTP Negotiate connections. A remote attacker could possibly use this issue to obtain sensitive information. (CVE-2026-5545)

It was discovered that curl incorrectly reused certain SMB connections. A remote attacker could possibly use this issue to obtain sensitive information. (CVE-2026-5773)

It was discovered that curl could leak proxy credentials when handling redirects in some configurations. A remote attacker could possibly use this issue to obtain sensitive information. (CVE-2026-6253)

It was discovered that curl could leak cookies because of stale custom cookie host handling in some requests. A remote attacker could possibly use this issue to obtain sensitive information. (CVE-2026-6276)

It was discovered that curl could leak .netrc credentials when reusing proxy connections in some situations. A remote attacker could possibly use this issue to obtain sensitive information. (CVE-2026-6429)

It was discovered that curl could leak Digest authentication state when switching proxies in some situations. A remote attacker could possibly use this issue to obtain sensitive information. (CVE-2026-7168)