Vulnerability in pymdown-extensions (CVE-2026-67422)
Summary
Vulnerability in pymdown-extensions (CVE-2026-67422). Risk of unauthorized operations or information disclosure. Exploitable via caret. Mitigation: upgrade to 10.16.1 or later.
Original description
The description as published by the source.
Summary
Four inline processors in pymdown-extensions contain regular expressions with
exponential backtracking. A single untrusted Markdown line under
50 bytes drives markdown.markdown() into unbounded CPU on the rendering thread
(seconds at ~45 bytes, growing exponentially with each added character). All four
fire in the extension's default configuration
and are reachable through the documented public API. The caret/tilde/
betterem blow-up was introduced by the emphasis-pattern rewrite in PR #2547
(first released in 10.13, Dec 2024) — earlier releases used a linear
(.+?) / ([^\s]+?) content group — and is present through 11.0 (latest);
magiclink's host pattern is long-standing and affects effectively all releases.
Likely CWE-1333 (Inefficient Regular Expression Complexity).
This is a distinct issue from CVE-2025-68142 (ReDoS in pymdownx.blocks.caption,
RE_FIG_NUM, fixed in 10.16.1): different extensions, different regexes, and a
different root cause (delimiter-run partition ambiguity rather than a ./\.
typo).
Details
Four regexes share, or closely mirror, a vulnerable shape — an inner group that
can partition a run of the delimiter character into {2,}-sized pieces in
exponentially many ways, wrapped in a lazy +? that must fail before the engine
can give up:
| Extension | Regex | Location (11.0) |
|---|---|---|
pymdownx.caret (superscript ^…^) |
SUP2 |
pymdownx/caret.py:56 |
pymdownx.tilde (subscript ~…~… |
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-67422 has been found in pymdown-extensions.
Attackers can target a specific entry point like caret over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade pymdown-extensions to 10.16.1 or later.
If unsure, ask your IT team or search "pymdown-extensions CVE-2026-67422" on the vendor's site.
CVE-2026-67422 (pymdown-extensions) — CWE-1333 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: caret / tilde / betterem / magiclink
Patched: 10.16.1 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-1333) exists in pymdown-extensions. Attackers reach the vulnerable code path via caret without authentication.
Check the vendor advisory for the affected versions of pymdown-extensions. Attack surface: caret / tilde / betterem / magiclink.
Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.
Update to 10.16.1.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'pymdown-extensions' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'pymdown-extensions' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
pymdown-extensionsを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade pymdown-extensions to 10.16.1ステージング環境で 10.16.1 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-67422 pymdown-extensions
- Ubuntu UBUNTU-CVE-2026-67422 pymdown-extensions
References
- advisory nvd.nist.gov
- advisory github.com
- package github.com
- package pypi.org
- web github.com
- web github.com