CVE-2026-97689

urllib3 is an HTTP client library for Python. From 1.10.3 until 2.8.0, the HTTPResponse.read_chunked and HTTPResponse.stream methods can allocate unbounded memory because the streaming chunk parser buffers the chunk-size field until newline or EOF without a length bound. The trigger is that a malicious server returns Transfer-Encoding: chunked followed by a very long run of bytes without a newline. The attack mechanism is that a malicious HTTP server sends a very long unterminated chunk-size line. The impact is that unbounded memory allocation can exhaust the client process. This issue is fixed in version 2.8.0.

Impact

urllib3's streaming API is designed for efficiently handling large HTTP responses by reading the content in chunks, rather than loading the entire response body into memory at once. When decoding a chunked-transfer-encoded response, this API reads each chunk's size field by buffering until it sees \n or EOF.

A malicious HTTP server can return Transfer-Encoding: chunked and then send a very long run of bytes without any newline, causing the streaming client to buffer that entire run before urllib3 can reject the chunk size as invalid and allocate more memory than intended.

To fix the issue, we'll reject chunk-size fields larger than 65536 bytes, as already done in the non-streaming case, which is currently handled by the Python standard library. Note that this only applies to reading the chunk-size field, not the chunk data, which is already handled correctly. Thus, there shouldn't be any impact for non-malicious servers.

Affected usages

Applications and libraries using urllib3 versions earlier than 2.8.0 may be affected when streaming a chunked response from untrusted sources. Specifically, this affects the read_chunked() and stream() methods of the HTTPResponse object.

This also affects requests streaming API, which uses urllib3 under the hood.

Remediation

Upgrade to urllib3 version 2.8.0 or later, where chunk-size fields larger than 65536 will be rejected. If upgrading is not immediately possible, consider reading the response at once using the read() method.

Sanity-friendly HTTP client for Python

Security Fix(es):

urllib3 is an HTTP client library for Python. From 1.10.3 until 2.8.0, the HTTPResponse.read_chunked and HTTPResponse.stream methods can allocate unbounded memory because the streaming chunk parser buffers the chunk-size field until newline or EOF without a length bound. The trigger is that a malicious server returns Transfer-Encoding: chunked followed by a very long run of bytes without a newline. The attack mechanism is that a malicious HTTP server sends a very long unterminated chunk-size line. The impact is that unbounded memory allocation can exhaust the client process. This issue is fixed in version 2.8.0.(CVE-2026-97689)

Sanity-friendly HTTP client for Python

Security Fix(es):

urllib3 is an HTTP client library for Python. From 1.10.3 until 2.8.0, the HTTPResponse.read_chunked and HTTPResponse.stream methods can allocate unbounded memory because the streaming chunk parser buffers the chunk-size field until newline or EOF without a length bound. The trigger is that a malicious server returns Transfer-Encoding: chunked followed by a very long run of bytes without a newline. The attack mechanism is that a malicious HTTP server sends a very long unterminated chunk-size line. The impact is that unbounded memory allocation can exhaust the client process. This issue is fixed in version 2.8.0.(CVE-2026-97689)

Sanity-friendly HTTP client for Python

Security Fix(es):

urllib3 is an HTTP client library for Python. From 1.10.3 until 2.8.0, the HTTPResponse.read_chunked and HTTPResponse.stream methods can allocate unbounded memory because the streaming chunk parser buffers the chunk-size field until newline or EOF without a length bound. The trigger is that a malicious server returns Transfer-Encoding: chunked followed by a very long run of bytes without a newline. The attack mechanism is that a malicious HTTP server sends a very long unterminated chunk-size line. The impact is that unbounded memory allocation can exhaust the client process. This issue is fixed in version 2.8.0.(CVE-2026-97689)

Sanity-friendly HTTP client for Python

Security Fix(es):

urllib3 is an HTTP client library for Python. From 1.26.0 until 2.8.0, the proxy_ssl_context, proxy_assert_hostname, proxy_assert_fingerprint, ssl_context, cert_reqs, verify_mode, use_forwarding_for_https=True, and CERT_NONE configuration paths fail to remain separated because target-server TLS settings are incorrectly applied to the HTTPS proxy connection. The trigger is that an application uses an HTTPS proxy and configures target-server TLS settings that must remain separate from the proxy TLS handshake, including HTTPS forwarding with target-specific identity or credentials. Applying cert_reqs=CERT_NONE can overwrite proxy_ssl_context.verify_mode in place, and the mutation persists so later connections reusing the same context may connect to the HTTPS proxy without certificate verification. The attack mechanism is that an attacker intercepts and impersonates the HTTPS proxy after the effective proxy policy accepts the attacker's certificate. The impact is that the attacker can observe or modify forwarded traffic or receive a target TLS client certificate, while CONNECT tunneling still preserves the separate end-to-end target TLS connection. This issue is fixed in version 2.8.0.(CVE-2026-97687)

urllib3 is an HTTP client library for Python. From 1.10.3 until 2.8.0, the HTTPResponse.read_chunked and HTTPResponse.stream methods can allocate unbounded memory because the streaming chunk parser buffers the chunk-size field until newline or EOF without a length bound. The trigger is that a malicious server returns Transfer-Encoding: chunked followed by a very long run of bytes without a newline. The attack mechanism is that a malicious HTTP server sends a very long unterminated chunk-size line. The impact is that unbounded memory allocation can exhaust the client process. This issue is fixed in version 2.8.0.(CVE-2026-97689)

Impact

urllib3's streaming API is designed for efficiently handling large HTTP responses by reading the content in chunks, rather than loading the entire response body into memory at once. When decoding a chunked-transfer-encoded response, this API reads each chunk's size field by buffering until it sees \n or EOF.

A malicious HTTP server can return Transfer-Encoding: chunked and then send a very long run of bytes without any newline, causing the streaming client to buffer that entire run before urllib3 can reject the chunk size as invalid and allocate more memory than intended.

To fix the issue, we'll reject chunk-size fields larger than 65536 bytes, as already done in the non-streaming case, which is currently handled by the Python standard library. Note that this only applies to reading the chunk-size field, not the chunk data, which is already handled correctly. Thus, there shouldn't be any impact for non-malicious servers.

Affected usages

Applications and libraries using urllib3 versions earlier than 2.8.0 may be affected when streaming a chunked response from untrusted sources. Specifically, this affects the read_chunked() and stream() methods of the HTTPResponse object.

This also affects requests streaming API, which uses urllib3 under the hood.

Remediation

Upgrade to urllib3 version 2.8.0 or later, where chunk-size fields larger than 65536 will be rejected. If upgrading is not immediately possible, consider reading the response at once using the read() method.

Python is an interpreted, interactive, object-oriented programming language, which includes modules, classes, exceptions, very high level dynamic data types and dynamic typing. Python supports interfaces to many system calls and libraries, as well as to various windowing systems.

Security Fix(es):

• urllib3: urllib3: Denial of Service via unbounded memory allocation in chunk parser (CVE-2026-97689)

• urllib3: urllib3: Traffic interception via HTTPS proxy TLS configuration override (CVE-2026-97687)

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.

Python is an interpreted, interactive, object-oriented programming language, which includes modules, classes, exceptions, very high level dynamic data types and dynamic typing. Python supports interfaces to many system calls and libraries, as well as to various windowing systems.

Security Fix(es):

• urllib3: urllib3: Denial of Service via unbounded memory allocation in chunk parser (CVE-2026-97689)

• urllib3: urllib3: Traffic interception via HTTPS proxy TLS configuration override (CVE-2026-97687)

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.

Python is an interpreted, interactive, object-oriented programming language, which includes modules, classes, exceptions, very high level dynamic data types and dynamic typing. Python supports interfaces to many system calls and libraries, as well as to various windowing systems.

Security Fix(es):

• urllib3: urllib3: Denial of Service via unbounded memory allocation in chunk parser (CVE-2026-97689)

• urllib3: urllib3: Traffic interception via HTTPS proxy TLS configuration override (CVE-2026-97687)

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.

Python is an interpreted, interactive, object-oriented programming language, which includes modules, classes, exceptions, very high level dynamic data types and dynamic typing. Python supports interfaces to many system calls and libraries, as well as to various windowing systems.

Security Fix(es):

• urllib3: urllib3: Denial of Service via unbounded memory allocation in chunk parser (CVE-2026-97689)

• urllib3: urllib3: Traffic interception via HTTPS proxy TLS configuration override (CVE-2026-97687)

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.

Python is an interpreted, interactive, object-oriented programming language, which includes modules, classes, exceptions, very high level dynamic data types and dynamic typing. Python supports interfaces to many system calls and libraries, as well as to various windowing systems.

Security Fix(es):

• urllib3: urllib3: Denial of Service via unbounded memory allocation in chunk parser (CVE-2026-97689)

• urllib3: urllib3: Traffic interception via HTTPS proxy TLS configuration override (CVE-2026-97687)

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.

Python is an interpreted, interactive, object-oriented programming language, which includes modules, classes, exceptions, very high level dynamic data types and dynamic typing. Python supports interfaces to many system calls and libraries, as well as to various windowing systems.

Security Fix(es):

• urllib3: urllib3: Denial of Service via unbounded memory allocation in chunk parser (CVE-2026-97689)

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.

Python is an interpreted, interactive, object-oriented programming language, which includes modules, classes, exceptions, very high level dynamic data types and dynamic typing. Python supports interfaces to many system calls and libraries, as well as to various windowing systems.

Security Fix(es):

• urllib3: urllib3: Denial of Service via unbounded memory allocation in chunk parser (CVE-2026-97689)

• urllib3: urllib3: Traffic interception via HTTPS proxy TLS configuration override (CVE-2026-97687)

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.

urllib3 is an HTTP client library for Python. From 1.10.3 until 2.8.0, the HTTPResponse.read_chunked and HTTPResponse.stream methods can allocate unbounded memory because the streaming chunk parser buffers the chunk-size field until newline or EOF without a length bound. The trigger is that a malicious server returns Transfer-Encoding: chunked followed by a very long run of bytes without a newline. The attack mechanism is that a malicious HTTP server sends a very long unterminated chunk-size line. The impact is that unbounded memory allocation can exhaust the client process. This issue is fixed in version 2.8.0.

Python is an interpreted, interactive, object-oriented programming language, which includes modules, classes, exceptions, very high level dynamic data types and dynamic typing. Python supports interfaces to many system calls and libraries, as well as to various windowing systems.

Security Fix(es):

• urllib3: urllib3: Denial of Service via unbounded memory allocation in chunk parser (CVE-2026-97689)
• urllib3: urllib3: Traffic interception via HTTPS proxy TLS configuration override (CVE-2026-97687)

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.

Python is an interpreted, interactive, object-oriented programming language, which includes modules, classes, exceptions, very high level dynamic data types and dynamic typing. Python supports interfaces to many system calls and libraries, as well as to various windowing systems.

Security Fix(es):

• urllib3: urllib3: Denial of Service via unbounded memory allocation in chunk parser (CVE-2026-97689)
• urllib3: urllib3: Traffic interception via HTTPS proxy TLS configuration override (CVE-2026-97687)

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.

Python is an interpreted, interactive, object-oriented programming language, which includes modules, classes, exceptions, very high level dynamic data types and dynamic typing. Python supports interfaces to many system calls and libraries, as well as to various windowing systems.

Security Fix(es):

• urllib3: urllib3: Denial of Service via unbounded memory allocation in chunk parser (CVE-2026-97689)
• urllib3: urllib3: Traffic interception via HTTPS proxy TLS configuration override (CVE-2026-97687)

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.

Python is an interpreted, interactive, object-oriented programming language, which includes modules, classes, exceptions, very high level dynamic data types and dynamic typing. Python supports interfaces to many system calls and libraries, as well as to various windowing systems.

Security Fix(es):

• urllib3: urllib3: Denial of Service via unbounded memory allocation in chunk parser (CVE-2026-97689)
• urllib3: urllib3: Traffic interception via HTTPS proxy TLS configuration override (CVE-2026-97687)

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.

Python is an interpreted, interactive, object-oriented programming language, which includes modules, classes, exceptions, very high level dynamic data types and dynamic typing. Python supports interfaces to many system calls and libraries, as well as to various windowing systems.

Security Fix(es):

• urllib3: urllib3: Denial of Service via unbounded memory allocation in chunk parser (CVE-2026-97689)
• urllib3: urllib3: Traffic interception via HTTPS proxy TLS configuration override (CVE-2026-97687)

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.

Python is an interpreted, interactive, object-oriented programming language, which includes modules, classes, exceptions, very high level dynamic data types and dynamic typing. Python supports interfaces to many system calls and libraries, as well as to various windowing systems.

Security Fix(es):

• urllib3: urllib3: Denial of Service via unbounded memory allocation in chunk parser (CVE-2026-97689)

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.

Python is an interpreted, interactive, object-oriented programming language, which includes modules, classes, exceptions, very high level dynamic data types and dynamic typing. Python supports interfaces to many system calls and libraries, as well as to various windowing systems.

Security Fix(es):

• urllib3: urllib3: Denial of Service via unbounded memory allocation in chunk parser (CVE-2026-97689)
• urllib3: urllib3: Traffic interception via HTTPS proxy TLS configuration override (CVE-2026-97687)

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.

urllib3 is an HTTP client library for Python. From 1.10.3 until 2.8.0, the HTTPResponse.read_chunked and HTTPResponse.stream methods can allocate unbounded memory because the streaming chunk parser buffers the chunk-size field until newline or EOF without a length bound. The trigger is that a malicious server returns Transfer-Encoding: chunked followed by a very long run of bytes without a newline. The attack mechanism is that a malicious HTTP server sends a very long unterminated chunk-size line. The impact is that unbounded memory allocation can exhaust the client process. This issue is fixed in version 2.8.0.

urllib3 is an HTTP client library for Python. From 1.10.3 until 2.8.0, the HTTPResponse.read_chunked and HTTPResponse.stream methods can allocate unbounded memory because the streaming chunk parser buffers the chunk-size field until newline or EOF without a length bound. The trigger is that a malicious server returns Transfer-Encoding: chunked followed by a very long run of bytes without a newline. The attack mechanism is that a malicious HTTP server sends a very long unterminated chunk-size line. The impact is that unbounded memory allocation can exhaust the client process. This issue is fixed in version 2.8.0.

TuxCare rebuilt urllib3 to address 2 CVEs. Fixed in 2.0.7.post4+tuxcare.

TuxCare rebuilt urllib3 to address 2 CVEs. Fixed in 1.26.20.post5+tuxcare.

TuxCare rebuilt urllib3 to address 2 CVEs. Fixed in 1.26.4.post6+tuxcare.

TuxCare rebuilt urllib3 to address 2 CVEs. Fixed in 1.25.11.post8+tuxcare.

TuxCare rebuilt urllib3 to address 5 CVEs. Fixed in 2.5.0.post2+tuxcare.

These are all security issues fixed in the python313-urllib3-2.8.0-1.1 package on the GA media of openSUSE Tumbleweed.

These are all security issues fixed in the python313-urllib3_1-1.26.20-8.1 package on the GA media of openSUSE Tumbleweed.

This update for python-urllib3 fixes the following issues:

• CVE-2026-97687: traffic interception due to possible HTTPS proxy TLS configuration override (bsc#1283908).
• CVE-2026-97688: denial of service due to infinite loop during chunked Deflate decoding (bsc#1283909).
• CVE-2026-97689: denial of service due to unbounded memory allocation in chunk parser (bsc#1283910).

Root has patched CVE-2026-97689 in the urllib3 package for Root:PyPI. Multiple fixed versions available.

This update for python-urllib3 fixes the following issues:

• CVE-2026-97687: traffic interception due to possible HTTPS proxy TLS configuration override (bsc#1283908).
• CVE-2026-97688: denial of service due to infinite loop during chunked Deflate decoding (bsc#1283909).
• CVE-2026-97689: denial of service due to unbounded memory allocation in chunk parser (bsc#1283910).

This update for python-urllib3 fixes the following issues:

• CVE-2026-97687: traffic interception due to possible HTTPS proxy TLS configuration override (bsc#1283908).
• CVE-2026-97688: denial of service due to infinite loop during chunked Deflate decoding (bsc#1283909).
• CVE-2026-97689: denial of service due to unbounded memory allocation in chunk parser (bsc#1283910).

This update for python-urllib3 fixes the following issues:

• CVE-2026-97688: denial of service due to infinite loop during chunked Deflate decoding (bsc#1283909).
• CVE-2026-97689: denial of service due to unbounded memory allocation in chunk parser (bsc#1283910).

This update for python-urllib3 fixes the following issues:

• CVE-2026-97688: denial of service due to infinite loop during chunked Deflate decoding (bsc#1283909).
• CVE-2026-97689: denial of service due to unbounded memory allocation in chunk parser (bsc#1283910).

This update for python-urllib3 fixes the following issues:

• CVE-2026-97687: traffic interception due to possible HTTPS proxy TLS configuration override (bsc#1283908).
• CVE-2026-97688: denial of service due to infinite loop during chunked Deflate decoding (bsc#1283909).
• CVE-2026-97689: denial of service due to unbounded memory allocation in chunk parser (bsc#1283910).

This update for python-urllib3_1 fixes the following issues:

• CVE-2026-97687: traffic interception due to possible HTTPS proxy TLS configuration override (bsc#1283908).
• CVE-2026-97688: denial of service due to infinite loop during chunked Deflate decoding (bsc#1283909).
• CVE-2026-97689: denial of service due to unbounded memory allocation in chunk parser (bsc#1283910).

Yu-Fu Fu, Seth Larson and Yonatan Magier discovered that urllib3 did not correctly handle certain certificate validations. An attacker could possibly use this issue to observe or modify forwarded traffic. This issue only affected Ubuntu 26.04 LTS. (CVE-2026-97687)

Martin Desrumaux discovered that urllib3 did not correctly handle decoding certain deflate responses. An attacker could possibly use this issue to cause a denial of service. This issue only affected Ubuntu 26.04 LTS. (CVE-2026-97688)

It was discovered that urllib3 did not correctly handle certain memory operations. An attacker could possibly use this issue to cause a denial of service. (CVE-2026-97689)