CVE-2026-59848

A flaw was found in libssh. A malicious SFTP server can send responses for unknown request IDs that libssh clients keep queued indefinitely, causing unbounded memory growth and client-side denial of service.

libssh is a library which implements the SSH protocol. It can be used to implement client and server applications.

Security Fix(es):

• libssh: libssh: information disclosure via short GSSAPI Curve25519 public key (CVE-2026-59842)

• libssh: libssh: denial of service via zero advertised channel packet size (CVE-2026-59843)

• libssh: libssh: denial of service via oversized SFTP read length (CVE-2026-59844)

• libssh: libssh: denial of service via unchecked ProxyCommand fork() failure (CVE-2026-59845)

• libssh: libssh: information disclosure via ProxyCommand %r username expansion (CVE-2026-59846)

• libssh: libssh: integrity downgrade via OpenSSL AES-GCM tag verification (CVE-2026-59847)

• libssh: libssh: denial of service via SFTP responses with unknown request IDs (CVE-2026-59848)

• libssh: libssh: denial of service via automatic certificate authentication loop (CVE-2026-59849)

• libssh: libssh: use-after-free via data callbacks on closed channels (CVE-2026-59850)

• libssh: libssh: authentication bypass via missing GSSAPI principal check (CVE-2026-59851)

• libssh: libssh: stack buffer overflow in SFTP server longname construction (CVE-2026-15370)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

libssh is a library which implements the SSH protocol. It can be used to implement client and server applications.

Security Fix(es):

• libssh: libssh: denial of service via zero advertised channel packet size (CVE-2026-59843)

• libssh: libssh: denial of service via oversized SFTP read length (CVE-2026-59844)

• libssh: libssh: denial of service via unchecked ProxyCommand fork() failure (CVE-2026-59845)

• libssh: libssh: information disclosure via ProxyCommand %r username expansion (CVE-2026-59846)

• libssh: libssh: integrity downgrade via OpenSSL AES-GCM tag verification (CVE-2026-59847)

• libssh: libssh: denial of service via SFTP responses with unknown request IDs (CVE-2026-59848)

• libssh: libssh: use-after-free via data callbacks on closed channels (CVE-2026-59850)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

libssh is a library which implements the SSH protocol. It can be used to implement client and server applications.

Security Fix(es):

• libssh: libssh: denial of service via zero advertised channel packet size (CVE-2026-59843)

• libssh: libssh: denial of service via oversized SFTP read length (CVE-2026-59844)

• libssh: libssh: denial of service via unchecked ProxyCommand fork() failure (CVE-2026-59845)

• libssh: libssh: information disclosure via ProxyCommand %r username expansion (CVE-2026-59846)

• libssh: libssh: integrity downgrade via OpenSSL AES-GCM tag verification (CVE-2026-59847)

• libssh: libssh: denial of service via SFTP responses with unknown request IDs (CVE-2026-59848)

• libssh: libssh: use-after-free via data callbacks on closed channels (CVE-2026-59850)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

A flaw was found in libssh. A malicious SFTP server can send responses for unknown request IDs that libssh clients keep queued indefinitely, causing unbounded memory growth and client-side denial of service.

libssh is a library which implements the SSH protocol. It can be used to implement client and server applications.

Security Fix(es):

• libssh: libssh: information disclosure via short GSSAPI Curve25519 public key (CVE-2026-59842)
• libssh: libssh: denial of service via zero advertised channel packet size (CVE-2026-59843)
• libssh: libssh: denial of service via oversized SFTP read length (CVE-2026-59844)
• libssh: libssh: denial of service via unchecked ProxyCommand fork() failure (CVE-2026-59845)
• libssh: libssh: information disclosure via ProxyCommand %r username expansion (CVE-2026-59846)
• libssh: libssh: integrity downgrade via OpenSSL AES-GCM tag verification (CVE-2026-59847)
• libssh: libssh: denial of service via SFTP responses with unknown request IDs (CVE-2026-59848)
• libssh: libssh: denial of service via automatic certificate authentication loop (CVE-2026-59849)
• libssh: libssh: use-after-free via data callbacks on closed channels (CVE-2026-59850)
• libssh: libssh: authentication bypass via missing GSSAPI principal check (CVE-2026-59851)
• libssh: libssh: stack buffer overflow in SFTP server longname construction (CVE-2026-15370)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

libssh is a library which implements the SSH protocol. It can be used to implement client and server applications.

Security Fix(es):

• libssh: libssh: denial of service via zero advertised channel packet size (CVE-2026-59843)
• libssh: libssh: denial of service via oversized SFTP read length (CVE-2026-59844)
• libssh: libssh: denial of service via unchecked ProxyCommand fork() failure (CVE-2026-59845)
• libssh: libssh: information disclosure via ProxyCommand %r username expansion (CVE-2026-59846)
• libssh: libssh: integrity downgrade via OpenSSL AES-GCM tag verification (CVE-2026-59847)
• libssh: libssh: denial of service via SFTP responses with unknown request IDs (CVE-2026-59848)
• libssh: libssh: use-after-free via data callbacks on closed channels (CVE-2026-59850)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

libssh is a library which implements the SSH protocol. It can be used to implement client and server applications.

Security Fix(es):

• libssh: libssh: denial of service via zero advertised channel packet size (CVE-2026-59843)
• libssh: libssh: denial of service via oversized SFTP read length (CVE-2026-59844)
• libssh: libssh: denial of service via unchecked ProxyCommand fork() failure (CVE-2026-59845)
• libssh: libssh: information disclosure via ProxyCommand %r username expansion (CVE-2026-59846)
• libssh: libssh: integrity downgrade via OpenSSL AES-GCM tag verification (CVE-2026-59847)
• libssh: libssh: denial of service via SFTP responses with unknown request IDs (CVE-2026-59848)
• libssh: libssh: use-after-free via data callbacks on closed channels (CVE-2026-59850)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

A flaw was found in libssh. A malicious SFTP server can send responses for unknown request IDs that libssh clients keep queued indefinitely, causing unbounded memory growth and client-side denial of service.

• CVE-2026-59843: reject a peer-supplied maximum packet size of zero to prevent infinite loops in channel writes
• CVE-2026-59848: track outstanding SFTP request IDs and reject responses with unknown IDs to prevent unbounded client memory growth
• CVE-2026-59845: handle ProxyCommand fork failures before storing the PID to prevent cleanup from signaling unrelated processes

• CVE-2026-59845: check the fork() return code when starting a ProxyCommand so a failed fork is not stored as pid -1 and later killed as a process group
• CVE-2026-59843: reject a maximum packet size of 0 in SSH2_MSG_CHANNEL_OPEN and SSH2_MSG_CHANNEL_OPEN_CONFIRMATION and clamp channel writes on remote_maxpacket directly, avoiding the non-progressing loop in channel_write_common()
• CVE-2026-59848: track outstanding SFTP request IDs and reject responses carrying an unknown ID instead of queueing them indefinitely

Stack buffer overflow in SFTP server longname construction. (CVE-2026-15370) Denial of service via zero advertised channel packet size. (CVE-2026-59843) Denial of service via oversized SFTP read length. (CVE-2026-59844) Denial of service via unchecked ProxyCommand fork() failure. (CVE-2026-59845) Information disclosure via ProxyCommand %r username expansion. (CVE-2026-59846) Integrity downgrade via OpenSSL AES-GCM tag verification. (CVE-2026-59847) Denial of service via SFTP responses with unknown request IDs. (CVE-2026-59848) Denial of service via automatic certificate authentication loop. (CVE-2026-59849) Use-after-free via data callbacks on closed channels. (CVE-2026-59850)

These are all security issues fixed in the libssh-config-0.11.5-1.1 package on the GA media of openSUSE Tumbleweed.

This update for libssh fixes the following issues:

• CVE-2026-15370: stack buffer overflow in SFTP server longname construction (bsc#1272162).
• CVE-2026-59843: denial of service via zero advertised channel packet size (bsc#1272164).
• CVE-2026-59844: denial of service via oversized SFTP read length (bsc#1272165).
• CVE-2026-59845: denial of service via unchecked ProxyCommand fork() failure (bsc#1272166).
• CVE-2026-59846: information disclosure via ProxyCommand %r username expansion (bsc#1272167).
• CVE-2026-59847: integrity downgrade via OpenSSL AES-GCM tag verification (bsc#1272168).
• CVE-2026-59848: denial of service via SFTP responses with unknown request IDs (bsc#1272169).
• CVE-2026-59849: denial of service via automatic certificate authentication loop (bsc#1272170).
• CVE-2026-59850: use-after-free via data callbacks on closed channels (bsc#1272171).

Changes for libssh:

• Update to 0.11.5:

• Zero-initialize every ssh_string
• Fix compatibility with C23 / gcc16
• Fix multiple memory leaks, null checks, and error checks
• Validate peer public key in DH key exchange
• Avoid remote window overflow
• Avoid off-by-one overflow during kbdint authentication
• Avoid logging uninitialized sequence numbers
• Avoid double conversion of SFTP version number
• Send correct SFTP server version number
• Avoid handling repeated SFTP INIT messages
• Harmonize return values from SFTP server callbacks

• Update %suse_version checks for SLES 16.x (jsc#PED-15815)

This update for libssh fixes the following issues:

• CVE-2026-15370: stack buffer overflow in SFTP server longname construction (bsc#1272162).
• CVE-2026-59843: denial of service via zero advertised channel packet size (bsc#1272164).
• CVE-2026-59844: denial of service via oversized SFTP read length (bsc#1272165).
• CVE-2026-59845: denial of service via unchecked ProxyCommand fork() failure (bsc#1272166).
• CVE-2026-59846: information disclosure via ProxyCommand %r username expansion (bsc#1272167).
• CVE-2026-59847: integrity downgrade via OpenSSL AES-GCM tag verification (bsc#1272168).
• CVE-2026-59848: denial of service via SFTP responses with unknown request IDs (bsc#1272169).
• CVE-2026-59849: denial of service via automatic certificate authentication loop (bsc#1272170).
• CVE-2026-59850: use-after-free via data callbacks on closed channels (bsc#1272171).

Changes for libssh:

• Update to 0.11.5:

• Zero-initialize every ssh_string
• Fix compatibility with C23 / gcc16
• Fix multiple memory leaks, null checks, and error checks
• Validate peer public key in DH key exchange
• Avoid remote window overflow
• Avoid off-by-one overflow during kbdint authentication
• Avoid logging uninitialized sequence numbers
• Avoid double conversion of SFTP version number
• Send correct SFTP server version number
• Avoid handling repeated SFTP INIT messages
• Harmonize return values from SFTP server callbacks

• Update %suse_version checks for SLES 16.x (jsc#PED-15815)

This update for libssh fixes the following issues:

• CVE-2026-15370: stack buffer overflow in SFTP server longname construction (bsc#1272162).
• CVE-2026-59843: denial of service via zero advertised channel packet size (bsc#1272164).
• CVE-2026-59844: denial of service via oversized SFTP read length (bsc#1272165).
• CVE-2026-59845: denial of service via unchecked ProxyCommand fork() failure (bsc#1272166).
• CVE-2026-59846: information disclosure via ProxyCommand %r username expansion (bsc#1272167).
• CVE-2026-59847: integrity downgrade via OpenSSL AES-GCM tag verification (bsc#1272168).
• CVE-2026-59848: denial of service via SFTP responses with unknown request IDs (bsc#1272169).
• CVE-2026-59849: denial of service via automatic certificate authentication loop (bsc#1272170).
• CVE-2026-59850: use-after-free via data callbacks on closed channels (bsc#1272171).

Changes for libssh:

• Update to 0.11.5:

• Zero-initialize every ssh_string
• Fix compatibility with C23 / gcc16
• Fix multiple memory leaks, null checks, and error checks
• Validate peer public key in DH key exchange
• Avoid remote window overflow
• Avoid off-by-one overflow during kbdint authentication
• Avoid logging uninitialized sequence numbers
• Avoid double conversion of SFTP version number
• Send correct SFTP server version number
• Avoid handling repeated SFTP INIT messages
• Harmonize return values from SFTP server callbacks

• Update %suse_version checks for SLES 16.x (jsc#PED-15815)

This update for libssh fixes the following issues:

• CVE-2026-15370: stack buffer overflow in SFTP server longname construction (bsc#1272162).
• CVE-2026-59843: denial of service via zero advertised channel packet size (bsc#1272164).
• CVE-2026-59844: denial of service via oversized SFTP read length (bsc#1272165).
• CVE-2026-59845: denial of service via unchecked ProxyCommand fork() failure (bsc#1272166).
• CVE-2026-59846: information disclosure via ProxyCommand %r username expansion (bsc#1272167).
• CVE-2026-59847: integrity downgrade via OpenSSL AES-GCM tag verification (bsc#1272168).
• CVE-2026-59848: denial of service via SFTP responses with unknown request IDs (bsc#1272169).
• CVE-2026-59849: denial of service via automatic certificate authentication loop (bsc#1272170).
• CVE-2026-59850: use-after-free via data callbacks on closed channels (bsc#1272171).

Changes for libssh:

• Update to 0.11.5:

• Zero-initialize every ssh_string
• Fix compatibility with C23 / gcc16
• Fix multiple memory leaks, null checks, and error checks
• Validate peer public key in DH key exchange
• Avoid remote window overflow
• Avoid off-by-one overflow during kbdint authentication
• Avoid logging uninitialized sequence numbers
• Avoid double conversion of SFTP version number
• Send correct SFTP server version number
• Avoid handling repeated SFTP INIT messages
• Harmonize return values from SFTP server callbacks

• Update %suse_version checks for SLES 16.x (jsc#PED-15815)

This update for libssh fixes the following issues:

• CVE-2026-3731: denial of Service via out-of-bounds read in SFTP extension name handler (bsc#1259377).
• CVE-2026-59843: denial of service via zero advertised channel packet size (bsc#1272164).
• CVE-2026-59844: denial of service via oversized SFTP read length (bsc#1272165).
• CVE-2026-59845: denial of service via unchecked ProxyCommand fork() failure (bsc#1272166).
• CVE-2026-59846: information disclosure via ProxyCommand %r username expansion (bsc#1272167).
• CVE-2026-59847: integrity downgrade via OpenSSL AES-GCM tag verification (bsc#1272168).
• CVE-2026-59848: denial of service via SFTP responses with unknown request IDs (bsc#1272169).
• CVE-2026-59850: use-after-free via data callbacks on closed channels (bsc#1272171).

This update for libssh fixes the following issues

• CVE-2026-59843: denial of service via zero advertised channel packet size (bsc#1272164).
• CVE-2026-59844: denial of service via oversized SFTP read length (bsc#1272165).
• CVE-2026-59845: denial of service via unchecked ProxyCommand fork() failure (bsc#1272166).
• CVE-2026-59846: information disclosure via ProxyCommand %r username expansion (bsc#1272167).
• CVE-2026-59847: integrity downgrade via OpenSSL AES-GCM tag verification (bsc#1272168).
• CVE-2026-59848: denial of service via SFTP responses with unknown request IDs (bsc#1272169).
• CVE-2026-59850: use-after-free via data callbacks on closed channels (bsc#1272171).

This update for libssh fixes the following issues

• CVE-2026-3731: denial of service via out-of-bounds read in SFTP extension name handler (bsc#1259377).
• CVE-2026-59843: denial of service via zero advertised channel packet size (bsc#1272164).
• CVE-2026-59844: denial of service via oversized SFTP read length (bsc#1272165).
• CVE-2026-59845: denial of service via unchecked ProxyCommand fork() failure (bsc#1272166).
• CVE-2026-59846: information disclosure via ProxyCommand %r username expansion (bsc#1272167).
• CVE-2026-59847: integrity downgrade via OpenSSL AES-GCM tag verification (bsc#1272168).
• CVE-2026-59848: denial of service via SFTP responses with unknown request IDs (bsc#1272169).
• CVE-2026-59850: use-after-free via data callbacks on closed channels (bsc#1272171).

This update for libssh fixes the following issues:

• CVE-2026-59843: denial of service via zero advertised channel packet size (bsc#1272164).
• CVE-2026-59844: denial of service via oversized SFTP read length (bsc#1272165).
• CVE-2026-59845: denial of service via unchecked ProxyCommand fork() failure (bsc#1272166).
• CVE-2026-59846: information disclosure via ProxyCommand %r username expansion (bsc#1272167).
• CVE-2026-59847: integrity downgrade via OpenSSL AES-GCM tag verification (bsc#1272168).
• CVE-2026-59848: denial of service via SFTP responses with unknown request IDs (bsc#1272169).
• CVE-2026-59850: use-after-free via data callbacks on closed channels (bsc#1272171).

This update for libssh fixes the following issues:

• CVE-2026-59843: denial of service via zero advertised channel packet size (bsc#1272164).
• CVE-2026-59844: denial of service via oversized SFTP read length (bsc#1272165).
• CVE-2026-59845: denial of service via unchecked ProxyCommand fork() failure (bsc#1272166).
• CVE-2026-59846: information disclosure via ProxyCommand %r username expansion (bsc#1272167).
• CVE-2026-59847: integrity downgrade via OpenSSL AES-GCM tag verification (bsc#1272168).
• CVE-2026-59848: denial of service via SFTP responses with unknown request IDs (bsc#1272169).
• CVE-2026-59850: use-after-free via data callbacks on closed channels (bsc#1272171).

It was discovered that libssh had a stack buffer overflow in its SFTP server when constructing directory listing entries for long filenames. An attacker could possibly use this issue to cause libssh to crash or execute arbitrary code. This issue only affected Ubuntu 26.04 LTS. (CVE-2026-15370)

It was discovered that libssh did not correctly handle SSH channel open messages advertising a zero maximum packet size. An authenticated remote attacker could possibly use this issue to cause libssh to consume excessive CPU resources, leading to a denial of service. (CVE-2026-59843)

It was discovered that libssh did not correctly limit SFTP read request lengths in its server implementation. An authenticated remote attacker could possibly use this issue to cause libssh to allocate excessive memory, leading to a denial of service. This issue only affected Ubuntu 26.04 LTS. (CVE-2026-59844)

It was discovered that libssh did not correctly handle ProxyCommand fork() failures. A local attacker could possibly use this issue to cause a denial of service. (CVE-2026-59845)

It was discovered that libssh did not correctly sanitize shell metacharacters when expanding usernames in ProxyCommand strings. An attacker could possibly use this issue to obtain sensitive information. (CVE-2026-59846)

It was discovered that libssh had incorrect AES-GCM tag verification when built with the OpenSSL backend. A machine-in-the-middle attacker could possibly use this issue to modify encrypted traffic without detection. (CVE-2026-59847)

It was discovered that libssh did not correctly handle SFTP server responses for unknown request IDs. An attacker could possibly use this issue to cause libssh to use excessive memory, leading to a denial of service. (CVE-2026-59848)

It was discovered that libssh had logic errors in certificate-based authentication that could cause clients to loop indefinitely when certificates were rejected. An attacker could possibly use this issue to cause a denial of service. This issue only affected Ubuntu 26.04 LTS. (CVE-2026-59849)

It was discovered that libssh could invoke data callbacks on channels after they had been closed. An attacker could possibly use this issue to cause libssh to crash or execute arbitrary code. (CVE-2026-59850)