{"cve":"CVE-2026-33079","nvd":{"published":"2026-05-06T18:16:03.097","modified":"2026-10-26T19:10:00.163","status":"Deferred","description":"In 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.","cvss_v4":{"vector":"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","score":8.7},"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","score":7.5},"cwes":["CWE-1333"],"references":["https://github.com/lepture/mistune/blob/df23edd60b43b639d2e6760ef9dd3d618aa11c21/src/mistune/helpers.py#L20-L25","https://github.com/lepture/mistune/security/advisories/GHSA-8mp2-v27r-99xp","https://access.redhat.com/errata/RHSA-2026:43038","https://access.redhat.com/errata/RHSA-2026:60520","https://access.redhat.com/security/cve/CVE-2026-33079"],"products":[],"source":"nvd","synced_at":"2026-10-26T19:31:02.781428341+00:00"},"epss":{"cve":"CVE-2026-33079","score":0.00528,"percentile":0.44451,"date":"2026-10-26"},"kev":null,"osv":[{"id":"GHSA-8mp2-v27r-99xp","url":"https://osv.dev/vulnerability/GHSA-8mp2-v27r-99xp","summary":"Mistune has a ReDoS in LINK_TITLE_RE that allows denial of service via crafted Markdown input","modified":"2026-09-10T03:51:05.039110483Z","packages":[{"ecosystem":"PyPI","name":"mistune","purl":"pkg:pypi/mistune","ranges":[">=3.0.0a1 <3.2.1"],"fixed":["3.2.1"]}]},{"id":"PYSEC-2026-2651","url":"https://osv.dev/vulnerability/PYSEC-2026-2651","summary":"Mistune has a ReDoS in LINK_TITLE_RE that allows denial of service via crafted Markdown input","modified":"2026-07-13T16:31:51.187577679Z","packages":[{"ecosystem":"PyPI","name":"mistune","purl":"pkg:pypi/mistune","ranges":[">=3.0.0a1 <3.2.1"],"fixed":["3.2.1"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}