6.9
Medium
CVE-2026-121438 Mistune before 3.3.3 Denial of Service via Balanced Bracket Link Parsing
Description
Mistune before 3.3.3 contains a denial of service vulnerability in InlineParser.parse_link that allows attackers to cause quadratic CPU growth by supplying balanced nested brackets. Attackers can submit crafted Markdown with thousands of nested bracket pairs not forming a valid link, triggering repeated _contains_nested_link scans that exhaust CPU in parsing applications.
CVSS 4.0 detail
Vector CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:NExploitable remotely over the network, without an account and without any user action; the impact on data or service is limited.
- Attack vector
- Network
- Attack complexity
- Low
- Attack requirements
- None
- Privileges required
- None
- Interaction
- None
- Confidentiality
- None
- Integrity
- None
- Availability
- Low
- Confidentiality of other systems
- None
- Integrity of other systems
- None
- Availability of other systems
- None
Affected products and versions
| Product | Affected versions | Fixed in |
|---|---|---|
| mistune 3.3 | earliest → < 3.3.3 | 3.3.3 |
Other CVEs of mistune
The 28 CVEs of mistune →
CVE-2026-121437
Mistune from 3.3.0 before 3.3.4 contains a denial of service vulnerability that allows remote attackers to exhaust CPU…
8.7
High
CVE-2026-115354
Mistune before 3.3.0 contains a path traversal vulnerability in the opt-in Include directive that allows attackers to…
7.1
High
CVE-2026-115355
Mistune before 3.3.0 contains a path traversal vulnerability in the Include directive that allows attackers to read…
8.7
High
CVE-2026-115353
Mistune before 3.3.0 Path Traversal via include Directive
9.2
Critical