CVE-2025-69534

Python-Markdown version 3.8 contain a vulnerability where malformed HTML-like sequences can cause html.parser.HTMLParser to raise an unhandled AssertionError during Markdown parsing. Because Python-Markdown does not catch this exception, any application that processes attacker-controlled Markdown may crash. This enables remote, unauthenticated Denial of Service in web applications, documentation systems, CI/CD pipelines, and any service that renders untrusted Markdown. The issue was acknowledged by the vendor and fixed in version 3.8.1. This issue causes a remote Denial of Service in any application parsing untrusted Markdown, and can lead to Information Disclosure through uncaught exceptions.

Python-Markdown version 3.8 contain a vulnerability where malformed HTML-like sequences can cause html.parser.HTMLParser to raise an unhandled AssertionError during Markdown parsing. Because Python-Markdown does not catch this exception, any application that processes attacker-controlled Markdown may crash. This enables remote, unauthenticated Denial of Service in web applications, documentation systems, CI/CD pipelines, and any service that renders untrusted Markdown. The issue was acknowledged by the vendor and fixed in version 3.8.1. This issue causes a remote Denial of Service in any application parsing untrusted Markdown, and can lead to Information Disclosure through uncaught exceptions.

This is a Python implementation of John Gruber’s Markdown. It is almost completely compliant with the reference implementation, though there are a few known issues.

Security Fix(es):

Python-Markdown version 3.8 contain a vulnerability where malformed HTML-like sequences can cause html.parser.HTMLParser to raise an unhandled AssertionError during Markdown parsing. Because Python-Markdown does not catch this exception, any application that processes attacker-controlled Markdown may crash. This enables remote, unauthenticated Denial of Service in web applications, documentation systems, CI/CD pipelines, and any service that renders untrusted Markdown. The issue was acknowledged by the vendor and fixed in version 3.8.1. This issue causes a remote Denial of Service in any application parsing untrusted Markdown, and can lead to Information Disclosure through uncaught exceptions.(CVE-2025-69534)

This is a Python implementation of John Gruber’s Markdown. It is almost completely compliant with the reference implementation, though there are a few known issues.

Security Fix(es):

Python-Markdown version 3.8 contain a vulnerability where malformed HTML-like sequences can cause html.parser.HTMLParser to raise an unhandled AssertionError during Markdown parsing. Because Python-Markdown does not catch this exception, any application that processes attacker-controlled Markdown may crash. This enables remote, unauthenticated Denial of Service in web applications, documentation systems, CI/CD pipelines, and any service that renders untrusted Markdown. The issue was acknowledged by the vendor and fixed in version 3.8.1. This issue causes a remote Denial of Service in any application parsing untrusted Markdown, and can lead to Information Disclosure through uncaught exceptions.(CVE-2025-69534)

This is a Python implementation of John Gruber’s Markdown. It is almost completely compliant with the reference implementation, though there are a few known issues.

Security Fix(es):

Python-Markdown version 3.8 contain a vulnerability where malformed HTML-like sequences can cause html.parser.HTMLParser to raise an unhandled AssertionError during Markdown parsing. Because Python-Markdown does not catch this exception, any application that processes attacker-controlled Markdown may crash. This enables remote, unauthenticated Denial of Service in web applications, documentation systems, CI/CD pipelines, and any service that renders untrusted Markdown. The issue was acknowledged by the vendor and fixed in version 3.8.1. This issue causes a remote Denial of Service in any application parsing untrusted Markdown, and can lead to Information Disclosure through uncaught exceptions.(CVE-2025-69534)

This is a Python implementation of John Gruber’s Markdown. It is almost completely compliant with the reference implementation, though there are a few known issues.

Security Fix(es):

Python-Markdown version 3.8 contain a vulnerability where malformed HTML-like sequences can cause html.parser.HTMLParser to raise an unhandled AssertionError during Markdown parsing. Because Python-Markdown does not catch this exception, any application that processes attacker-controlled Markdown may crash. This enables remote, unauthenticated Denial of Service in web applications, documentation systems, CI/CD pipelines, and any service that renders untrusted Markdown. The issue was acknowledged by the vendor and fixed in version 3.8.1. This issue causes a remote Denial of Service in any application parsing untrusted Markdown, and can lead to Information Disclosure through uncaught exceptions.(CVE-2025-69534)

Python-Markdown version 3.8 contain a vulnerability where malformed HTML-like sequences can cause html.parser.HTMLParser to raise an unhandled AssertionError during Markdown parsing. Because Python-Markdown does not catch this exception, any application that processes attacker-controlled Markdown may crash. This enables remote, unauthenticated Denial of Service in web applications, documentation systems, CI/CD pipelines, and any service that renders untrusted Markdown. The issue was acknowledged by the vendor and fixed in version 3.8.1. This issue causes a remote Denial of Service in any application parsing untrusted Markdown, and can lead to Information Disclosure through uncaught exceptions.

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):

• python-markdown: denial of service via malformed HTML-like sequences (CVE-2025-69534)

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):

• python-markdown: denial of service via malformed HTML-like sequences (CVE-2025-69534)

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.

Root has patched CVE-2025-69534 in the rootio-Markdown package for Root:PyPI. Multiple fixed versions available.

Root has patched CVE-2025-69534 in the python3.9 package for Root:Debian:11. Multiple fixed versions available.

Root has patched CVE-2025-69534 in the python3.11 package for Root:Debian:12. Multiple fixed versions available.

Python-Markdown version 3.8 contain a vulnerability where malformed HTML-like sequences can cause html.parser.HTMLParser to raise an unhandled AssertionError during Markdown parsing. Because Python-Markdown does not catch this exception, any application that processes attacker-controlled Markdown may crash. This enables remote, unauthenticated Denial of Service in web applications, documentation systems, CI/CD pipelines, and any service that renders untrusted Markdown. The issue was acknowledged by the vendor and fixed in version 3.8.1. This issue causes a remote Denial of Service in any application parsing untrusted Markdown, and can lead to Information Disclosure through uncaught exceptions.

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):

• python-markdown: denial of service via malformed HTML-like sequences (CVE-2025-69534)

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):

• python-markdown: denial of service via malformed HTML-like sequences (CVE-2025-69534)

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.

• SECURITY UPDATE: unhandled NotImplementedError denial-of-service in the html.parser module when parsing malformed markup declarations
  • debian/patches/CVE-2025-69534.patch: narrow the marked-section dispatch in parse_html_declaration() in Lib/html/parser.py so only "<![CDATA[" is routed to parse_marked_section(); any other malformed "<!..." construct now falls through to parse_bogus_comment() instead of reaching ParserBase.error(), which raises NotImplementedError.
  • CVE-2025-69534

• SECURITY UPDATE: unhandled HTMLParseError denial of service in HTMLParser when parsing malformed markup declarations
  • debian/patches/CVE-2025-69534.patch: narrow the marked-section dispatch in parse_html_declaration() in Lib/HTMLParser.py so only "<![CDATA[" is routed to parse_marked_section(); any other malformed "<!..." construct now falls through to parse_bogus_comment() instead of raising HTMLParseError; also update the test_broken_condcoms expectations to match.
  • CVE-2025-69534

This update for python-Markdown fixes the following issue:

• CVE-2025-69534: incomplete markup declaration in raw HTML can crash applications that process untrusted Markdown (bsc#1259256).

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It was discovered that Python's HTMLParser incorrectly handled certain malformed HTML input. An attacker could possibly use this issue to cause Python to crash, resulting in a denial of service. This issue only affected Ubuntu 22.04 LTS and Ubuntu 24.04 LTS. (CVE-2025-69534)

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It was discovered that Python's webbrowser module accepted leading dashes in URLs, which could be interpreted as command-line options. An attacker could possibly use this issue to execute arbitrary commands. This issue only affected Ubuntu 22.04 LTS and Ubuntu 24.04 LTS. (CVE-2026-4519)

It was discovered that Python incorrectly handled webbrowser.open() handlers. An attacker could possibly use this issue to execute arbitrary commands. (CVE-2026-4786)

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It was discovered that Python's http.cookies module incorrectly escaped values in the js_output() method. An attacker could possibly use this issue to inject arbitrary JavaScript. (CVE-2026-6019)

It was discovered that Python's lzma, bz2, and gzip decompressor objects had a use-after-free vulnerability. An attacker could possibly use this issue to cause Python to crash or execute arbitrary code. (CVE-2026-6100)

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It was discovered that Python's bz2 module allowed reuse of a BZ2Decompressor object after a decompression error. An attacker could possibly use this issue to cause Python to crash or execute arbitrary code. (CVE-2026-9669)

It was discovered that Python incorrectly handled expanding environment variables in os.path.expandvars() when the input was user-controlled. An attacker could possibly use this issue to cause Python to consume resources, leading to a denial of service. (CVE-2025-6075)

It was discovered that Python incorrectly handled certain malformed HTML-like markup in the HTMLParser module, raising an uncaught exception. A remote attacker could possibly use this issue to cause applications that parse untrusted input to crash, resulting in a denial of service. (CVE-2025-69534)