Mistune ReDoS in LINK_TITLE_RE allows denial of service with crafted Markdown titles

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Summary

CVECVE-2026-33079
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-06 18:16:03 UTC
Updated2026-08-28 16:17:28 UTC
DescriptionIn versions 3.0.0a1 through 3.2.0 of Mistune, there is a ReDoS (Regular Expression Denial of Service) vulnerability in `LINK_TITLE_RE` that allows an attacker who can supply Markdown for parsing to cause denial of service. The regular expression used for parsing link titles contains overlapping alternatives that can trigger catastrophic backtracking. In both the double-quoted and single-quoted branches, a backslash followed by punctuation can be matched either as an escaped punctuation sequence or as two ordinary characters, creating an ambiguous pattern inside a repeated group. If an attacker supplies Markdown containing repeated ! sequences with no closing quote, the regex engine explores an exponential number of backtracking paths. This is reachable through normal Markdown parsing of inline links and block link reference definitions. A small crafted input can therefore cause significant CPU consumption and make applications using Mistune unresponsive.

Risk And Classification

Primary CVSS: v4.0 8.7 HIGH from [email protected]

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

EPSS: 0.005280000 probability, percentile 0.426060000 (date 2026-08-30)

Problem Types: CWE-1333 | CWE-1333 CWE-1333: Inefficient Regular Expression Complexity | CWE-1333 Inefficient Regular Expression Complexity

VersionSourceTypeScoreSeverityVector
4.0[email protected]Secondary8.7HIGHCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/C...
4.0CNADECLARED8.7HIGHCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
3.1ADPCVSS7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.10b0ca135-0b70-47e7-9f44-1890c2a1c46cSecondary7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
None
Privileges Required
None
User Interaction
None
Confidentiality
None
Integrity
None
Availability
High
Sub Conf.
None
Sub Integrity
None
Sub Availability
None

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Lepture Mistune affected >=3.0.0a1, <= 3.2.0 Not specified
ADP Red Hat Red Hat Migration Toolkit For Applications 8.2 unaffected 1784109883 * rpm Not specified
ADP Red Hat Red Hat OpenShift AI 3.4 unaffected 1787073866 * rpm Not specified
ADP Red Hat Red Hat OpenShift AI 3.4 unaffected 1787073936 * rpm Not specified
ADP Red Hat Red Hat OpenShift AI 3.4 unaffected 1787073873 * rpm Not specified
ADP Red Hat Red Hat OpenShift AI 3.4 unaffected 1787073459 * rpm Not specified
ADP Red Hat Red Hat OpenShift AI 3.4 unaffected 1787073611 * rpm Not specified
ADP Red Hat Red Hat OpenShift AI 3.4 unaffected 1787073451 * rpm Not specified
ADP Red Hat Red Hat OpenShift AI 3.4 unaffected 1787073451 * rpm Not specified
ADP Red Hat Red Hat OpenShift AI 3.4 unaffected 1787076778 * rpm Not specified
ADP Red Hat Red Hat OpenShift AI 3.4 unaffected 1787077779 * rpm Not specified
ADP Red Hat Red Hat OpenShift AI 3.4 unaffected 1787076481 * rpm Not specified
ADP Red Hat Red Hat OpenShift AI 3.4 unaffected 1787074331 * rpm Not specified
ADP Red Hat Red Hat OpenShift AI 3.4 unaffected 1787073913 * rpm Not specified
ADP Red Hat Red Hat OpenShift AI 3.4 unaffected 1787074078 * rpm Not specified
ADP Red Hat Red Hat OpenShift AI 3.4 unaffected 1787073929 * rpm Not specified
ADP Red Hat Red Hat OpenShift AI 3.4 unaffected 1787073605 * rpm Not specified
ADP Red Hat Red Hat OpenShift AI 3.4 unaffected 1787073546 * rpm Not specified
ADP Red Hat Red Hat OpenShift AI 3.4 unaffected 1787073717 * rpm Not specified
ADP Red Hat Red Hat OpenShift AI 3.4 unaffected 1787073713 * rpm Not specified
ADP Red Hat Red Hat OpenShift AI 3.4 unaffected 1787073593 * rpm Not specified
ADP Red Hat Red Hat OpenShift AI RHOAI Not specified Not specified
ADP Red Hat Red Hat OpenShift AI RHOAI Not specified Not specified
ADP Red Hat Red Hat OpenShift AI RHOAI Not specified Not specified
ADP Red Hat Red Hat Satellite 6 Not specified Not specified

References

ReferenceSourceLinkTags
access.redhat.com/errata/RHSA-2026:43038 0b0ca135-0b70-47e7-9f44-1890c2a1c46c access.redhat.com
github.com/lepture/mistune/security/advisories/GHSA-8mp2-v27r-99xp 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
bugzilla.redhat.com/show_bug.cgi 0b0ca135-0b70-47e7-9f44-1890c2a1c46c bugzilla.redhat.com
github.com/lepture/mistune/blob/df23edd60b43b639d2e6760ef9dd3d618aa11c21... [email protected] github.com
access.redhat.com/security/cve/CVE-2026-33079 0b0ca135-0b70-47e7-9f44-1890c2a1c46c access.redhat.com
security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33079.json 0b0ca135-0b70-47e7-9f44-1890c2a1c46c security.access.redhat.com
access.redhat.com/errata/RHSA-2026:60520 0b0ca135-0b70-47e7-9f44-1890c2a1c46c access.redhat.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Additional Advisory Data

SourceTimeEvent
ADP2026-05-06T18:01:13.818ZReported to Red Hat.
ADP2026-05-06T17:25:09.026ZMade public.

Solutions

ADP: RHSA-2026:43038: Red Hat Migration Toolkit for Applications 8.2

ADP: RHSA-2026:60520: Red Hat OpenShift AI 3.4

Workarounds

ADP: Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.

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