{"affected":[{"product":"libass","source":"CNA: GitHub_M","vendor":"libass","versions":[{"status":"affected","version":">= 0.17.4, < 0.17.5"}]}],"cveId":"CVE-2026-61626","cwes":["CWE-787"],"description":"libass is a portable subtitle renderer for the ASS/SSA (Advanced Substation Alpha/Substation Alpha) subtitle format. From 0.17.4 until 0.17.5, libass event pruning does not guard negative Matroska `ReadOrder` values, allowing an attacker to clear arbitrarily many bits to zero at attacker-controlled positions near the NULL pointer. Exploitation requires a malicious Matroska stream loaded through `ass_process_chunk`, enabled read-order checking, and later pruning of the malicious events. Read-order checking is enabled by default unless `ass_set_check_readorder` is called with zero; pruning must occur explicitly through `ass_prune_events` or through automatic pruning previously enabled with `ass_configure_prune`. On common systems with arithmetic right shift, 32-bit int values, the upper address region reserved to the kernel, and matching binary/kernel architecture, the expected consequence is denial of service. More extensive exploitation on uncommon systems is theoretical and strongly constrained by the target addresses, bit-clearing-only mutation, and ASLR. This issue is fixed in version 0.17.5.","epss":{"date":"2026-11-04","percentile":0.01738,"score":0.00118},"exploits":[],"kev":null,"metrics":[{"score":7.3,"severity":"high","source":"CNA: GitHub_M","vector":"CVSS:4.0/AV:L/AC:H/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N","version":"4.0"},{"score":7.3,"severity":"high","source":"NVD: security-advisories@github.com","vector":"CVSS:4.0/AV:L/AC:H/AT:N/PR:N/UI:P/VC:H/VI:H/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","version":"4.0"}],"modifiedAt":1793834276277,"publishedAt":1793371941006,"references":[{"source":"CNA: GitHub_M","tags":["x_refsource_CONFIRM"],"url":"https://github.com/libass/libass/security/advisories/GHSA-5gf7-wjfm-vmvm"},{"source":"CNA: GitHub_M","tags":["x_refsource_MISC"],"url":"https://github.com/libass/libass/commit/23da65a130bb8c5b2cf0c7df0dd7d424607f98f1"},{"source":"CNA: GitHub_M","tags":["x_refsource_MISC"],"url":"https://github.com/libass/libass/releases/tag/0.17.5"},{"source":"security-advisories@github.com","tags":[],"url":"https://github.com/libass/libass/commit/23da65a130bb8c5b2cf0c7df0dd7d424607f98f1"},{"source":"security-advisories@github.com","tags":[],"url":"https://github.com/libass/libass/releases/tag/0.17.5"},{"source":"security-advisories@github.com","tags":[],"url":"https://github.com/libass/libass/security/advisories/GHSA-5gf7-wjfm-vmvm"}],"remediation":[],"revision":"b925b2b068198dab5ff3493299364edda5756a192aa2af9a1a3f1f2d34f8baa7","sources":[{"modifiedAt":1793832305471,"name":"CNA: GitHub_M","retrievedAt":1793833909824,"url":"https://www.cve.org/CVERecord?id=CVE-2026-61626"},{"modifiedAt":1793834276277,"name":"NVD","retrievedAt":1793838189489,"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-61626"},{"modifiedAt":null,"name":"FIRST EPSS","retrievedAt":1793833913156,"url":"https://api.first.org/data/v1/epss?cve=CVE-2026-61626"}],"ssvc":{"assessedAt":1793832269050,"automatable":"yes","exploitation":"none","source":"ADP: CISA-ADP","technicalImpact":"total"},"status":"published","title":"libass: Out-of-bounds bit clears for negative Matroska ReadOrder values","updatedAt":1793838189489}