Denial of service in Python-Markdown via unmatched link brackets
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Attack requirements
- None
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- None · None · High
- Fix status
- No fix listed
Attack profile from CVSS 4.0 · CNA. Fix status from CNA and Red Hat. Impact type from CWE-407.
Summary
Python-Markdown from 3.0 through 3.11.2 contains an algorithmic complexity flaw in its inline link parsing, classified as CWE-407. A remote attacker without privileges can submit short Markdown with repeated unmatched brackets to exhaust CPU, keeping workers busy for minutes.
Written with Claude Haiku 5.5 from the sources below · 2026-11-03
Description from the CNA
Python-Markdown 3.0 through 3.11.2 contains an algorithmic complexity vulnerability in inline link parsing that allows remote attackers to exhaust CPU through unmatched brackets. Attackers can submit short Markdown containing repeated [ or ![ characters, forcing LinkInlineProcessor.getText() and getLink() into quadratic scans that keep workers busy for minutes.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- Poc
- Automatable
- Yes
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Python-Markdown | Markdown | 3.0 – 3.11.2 | — | No fix listed | CNA |
- Markdown VendorPython-Markdown Affected 3.0 – 3.11.2 Fixed in — No fix listed CNA
Remediation
No fixed version is listed for Python-Markdown. Red Hat lists no plan available for Red Hat AI Inference Server, Red Hat Ansible Automation Platform 2, Red Hat Developer Hub 1, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8 and other products.
Written with Claude Haiku 5.5 from the sources below · 2026-11-03
Vendor assessments
Red Hat
Red Hat rating: Important. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat AI Inference Server | Affected | No fix yet |
| Red Hat Ansible Automation Platform 2 | Affected | No fix yet |
| Red Hat Developer Hub 1 | Affected | No fix yet |
| Red Hat Enterprise Linux 10 | Affected | No fix yet |
| Red Hat Enterprise Linux 8 | Affected | No fix yet |
| Red Hat Enterprise Linux 9 | Affected | No fix yet |
| Red Hat Enterprise Linux AI (RHEL AI) 3 | Affected | No fix yet |
| Red Hat OpenShift AI (RHOAI) | Affected | No fix yet |
| Red Hat OpenShift Container Platform 4 | Affected | No fix yet |
| Red Hat Satellite 6 | Affected | No fix yet |
| Red Hat Trusted Artifact Signer | Affected | No fix yet |
| Self-service automation portal 2 | Affected | No fix yet |
Not affected: 1 product
- Red Hat OpenShift AI (RHOAI)
Timeline
- 2026-10-29 Threatist record created from CVE-2019-25781
- 2026-10-29 Alias added: GHSA-4g9h-pv2v-fw83
- 2026-10-30 Affected versions changed · Red Hat
- 2026-10-30 CVSS score added · Red Hat
- 2026-10-30 Affected versions changed · Red Hat
- 2026-10-31 Priority changed: MEDIUM → LOW
- 2026-11-03 CISA SSVC decision points changed
- 2026-11-03 Priority changed: LOW → HIGH
References
More Python-Markdown vulnerabilities
- TI-2025-42876 Python-Markdown version 3.8 contain a vulnerability where malformed HTML-like sequences… CVSS 3.1HIGH 7.5
Sources
- CVE-2019-25781 · CVE Program
- CVE-2019-25781 · NVD
- FIRST EPSS
- GHSA-4g9h-pv2v-fw83 · GitHub Advisory Database · CC BY 4.0
- CVE-2019-25781 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences