CVE-2025-69534 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in markdown. A fix is available for markdown — see the affected versions and patch details below.
Python-Markdown has an Uncaught Exception
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for CVE-2025-69534.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2025-69534 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
markdownReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | markdown | all versions | 3.8.1pip install --upgrade 'markdown==3.8.1' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for markdown, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update markdown to 3.8.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-69534 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2025-69534 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2025-69534. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
To exploit this flaw, an attacker must be able to supply a specially crafted payload to be processed by an application using Python-Markdown. Additionally, the security impact of this vulnerability is limited to an information disclosure via the unhandled exception stack trace and a denial of service. There is no…
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Ansible Automation Platform 2.5 for RHEL 8 | python3.12-markdown-0:3.10.2-1.el8ap | RHSA-2026:13512 |
| Red Hat Ansible Automation Platform 2.6 for RHEL 9 | automation-controller-0:4.7.11-2.el9ap | RHSA-2026:13508 |
| Red Hat Enterprise Linux 10 | python-markdown-0:3.5.1-6.el10_2.1 | RHSA-2026:19155 |
| Red Hat Enterprise Linux 10.0 Extended Update Support | python-markdown-0:3.5.1-6.el10_0.1 | RHSA-2026:20677 |
| Red Hat Enterprise Linux 9 | python-markdown-0:3.3.4-4.el9_8.2 | RHSA-2026:19366 |
| Red Hat Enterprise Linux 9.4 Extended Update Support | python-markdown-0:3.3.4-4.el9_4.2 | RHSA-2026:20674 |
| Red Hat Enterprise Linux 9.6 Extended Update Support | python-markdown-0:3.3.4-4.el9_6.2 | RHSA-2026:20676 |
| Red Hat Satellite 6.16 for RHEL 8 | python-markdown-0:3.8.2-1.el8pc | RHSA-2026:14874 |
Frequently Asked Questions
Is CVE-2025-69534 in your dependencies?
O3 Security finds CVE-2025-69534 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.