{"id":"CVE-2026-61626","state":"PUBLISHED","title":"libass: Out-of-bounds bit clears for negative Matroska ReadOrder values","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.","publishedAt":"2026-10-30T14:52:21.006Z","updatedAt":"2026-10-30T14:52:21.006Z","severity":{"score":7.3,"label":"High","version":"4.0","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","source":"GitHub_M"},"assigner":"GitHub_M","products":["libass libass"],"affected":[{"vendor":"libass","product":"libass","versions":[{"version":">= 0.17.4, < 0.17.5","status":"affected"}]}],"references":["https://github.com/libass/libass/security/advisories/GHSA-5gf7-wjfm-vmvm","https://github.com/libass/libass/commit/23da65a130bb8c5b2cf0c7df0dd7d424607f98f1","https://github.com/libass/libass/releases/tag/0.17.5"],"weaknesses":["CWE-787"],"ingestedAt":"2026-10-30T15:02:06.750Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/61xxx/CVE-2026-61626.json","commit":"febef872f3cfb6eaadc9eb08e2a31cb15b3d216f","baselineCommit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-61626","state":"PUBLISHED","datePublished":"2026-10-30T14:52:21.006Z","dateUpdated":"2026-10-30T14:52:21.006Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-07-10T17:38:57.110Z"},"containers":{"cna":{"title":"libass: Out-of-bounds bit clears for negative Matroska ReadOrder values","descriptions":[{"lang":"en","value":"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."}],"affected":[{"vendor":"libass","product":"libass","versions":[{"version":">= 0.17.4, < 0.17.5","status":"affected"}]}],"references":[{"url":"https://github.com/libass/libass/security/advisories/GHSA-5gf7-wjfm-vmvm","name":"https://github.com/libass/libass/security/advisories/GHSA-5gf7-wjfm-vmvm","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/libass/libass/commit/23da65a130bb8c5b2cf0c7df0dd7d424607f98f1","name":"https://github.com/libass/libass/commit/23da65a130bb8c5b2cf0c7df0dd7d424607f98f1","tags":["x_refsource_MISC"]},{"url":"https://github.com/libass/libass/releases/tag/0.17.5","name":"https://github.com/libass/libass/releases/tag/0.17.5","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV4_0":{"attackVector":"LOCAL","attackComplexity":"HIGH","attackRequirements":"NONE","privilegesRequired":"NONE","userInteraction":"PASSIVE","vulnConfidentialityImpact":"HIGH","vulnIntegrityImpact":"HIGH","vulnAvailabilityImpact":"HIGH","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","subAvailabilityImpact":"NONE","baseScore":7.3,"baseSeverity":"HIGH","vectorString":"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"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-787","lang":"en","description":"CWE-787: Out-of-bounds Write","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-10-30T14:52:21.006Z"},"source":{"advisory":"GHSA-5gf7-wjfm-vmvm","discovery":"UNKNOWN"}}}}}