{"id":"CVE-2026-61626","aliases":["DEBIAN-CVE-2026-61626","EUVD-2026-114006","GHSA-5gf7-wjfm-vmvm","UBUNTU-CVE-2026-61626","USN-8815-1"],"status":"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.","severity":{"version":"4.0","score":7.3,"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","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.00118,"percentile":0.01742,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-787"],"published":"2026-07-14T00:00:00Z","modified":"2026-11-06T01:07:17Z","fixes":[{"ecosystem":"Debian:14","package":"libass","fixed_in":["1:0.17.5-1"],"sources":["osv"]},{"ecosystem":"Ubuntu:Pro:26.04:LTS","package":"libass","fixed_in":["1:0.17.4-2ubuntu0.1~esm1"],"sources":["osv"]}],"affected":[{"source":"osv","ecosystem":"Debian:14","package":"libass","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1:0.17.5-1"}]}],"versions":["1:0.17.3-1","1:0.17.4-1","1:0.17.4-2"]},{"source":"osv","ecosystem":"Ubuntu:Pro:26.04:LTS","package":"libass","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1:0.17.4-2ubuntu0.1~esm1"}]}],"versions":["1:0.17.3-1","1:0.17.4-2"]},{"source":"osv","ecosystem":"Ubuntu:Pro:14.04:LTS","package":"libass","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.10.1-3ubuntu1+esm2"}]}],"versions":["0.10.1-1ubuntu1","0.10.1-3","0.10.1-3ubuntu1","0.10.1-3ubuntu1+esm1"],"bundled":4},{"source":"osv","ecosystem":"Ubuntu:Pro:18.04:LTS","package":"libass","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1:0.14.0-1ubuntu0.1~esm1"}]}],"versions":["1:0.13.7-2","1:0.14.0-1"],"bundled":4},{"source":"osv","ecosystem":"Ubuntu:Pro:20.04:LTS","package":"libass","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1:0.14.0-2ubuntu0.1~esm1"}]}],"versions":["1:0.14.0-2"],"bundled":4},{"source":"osv","ecosystem":"Ubuntu:Pro:24.04:LTS","package":"libass","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1:0.17.1-2ubuntu0.1~esm1"}]}],"versions":["1:0.17.1-1","1:0.17.1-2","1:0.17.1-2build1"],"bundled":4},{"source":"osv","ecosystem":"Ubuntu:Pro:26.04:LTS","package":"libass","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1:0.17.4-2ubuntu0.1~esm1"}]}],"versions":["1:0.17.3-1","1:0.17.4-2"],"bundled":4}],"products":[{"vendor":"libass","product":"libass"}],"references":[{"url":"https://github.com/libass/libass/security/advisories/GHSA-5gf7-wjfm-vmvm","tags":["x_refsource_CONFIRM","advisory","report"]},{"url":"https://github.com/libass/libass/commit/23da65a130bb8c5b2cf0c7df0dd7d424607f98f1","tags":["x_refsource_MISC","fix"]},{"url":"https://github.com/libass/libass/releases/tag/0.17.5","tags":["x_refsource_MISC","web"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/61xxx/CVE-2026-61626.json","tags":["advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-61626","tags":["advisory"]},{"url":"https://security-tracker.debian.org/tracker/CVE-2026-61626","tags":["advisory"]},{"url":"https://ubuntu.com/security/CVE-2026-61626","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-61626","tags":["report"]},{"url":"https://github.com/libass/libass/issues/937","tags":["report"]},{"url":"https://ubuntu.com/security/notices/USN-8815-1","tags":["advisory"]},{"url":"https://ubuntu.com/security/CVE-2020-24994","tags":["report"]},{"url":"https://ubuntu.com/security/CVE-2020-26682","tags":["report"]},{"url":"https://ubuntu.com/security/CVE-2026-61627","tags":["report"]}],"sources":{"cve":[{"id":"CVE-2026-61626","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.","status":"published","published":"2026-10-30T14:52:21.006Z","modified":"2026-11-04T22:45:05.471Z","cvss":[{"version":"4.0","score":7.3,"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","level":"high","assessor":"cna"}],"cwes":["CWE-787"],"updated_at":"2026-11-04T23:40:09.798467Z"}],"euvd":[{"id":"EUVD-2026-114006","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.","status":"published","published":"2026-10-30T14:52:21Z","modified":"2026-11-04T22:45:05Z","cvss":[{"version":"4.0","score":7.3,"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","level":"high"}],"updated_at":"2026-11-05T00:47:41.139684Z"}],"nvd":[{"id":"CVE-2026-61626","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.","status":"published","published":"2026-10-30T15:16:52.5Z","modified":"2026-11-04T23:17:56.277Z","cvss":[{"version":"4.0","score":7.3,"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","level":"high","assessor":"secondary"}],"cwes":["CWE-787"],"updated_at":"2026-11-05T01:45:13.601219Z"}],"osv":[{"id":"CVE-2026-61626","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.","status":"published","published":"2026-10-30T14:52:21.006Z","modified":"2026-11-06T01:07:17.702091343Z","cvss":[{"version":"4.0","score":7.3,"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","level":"high"}],"cwes":["CWE-787"],"updated_at":"2026-11-06T01:32:47.895286Z"},{"id":"DEBIAN-CVE-2026-61626","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.","status":"published","published":"2026-10-30T15:16:52.5Z","modified":"2026-11-05T09:47:39.493430395Z","cvss":[{"version":"4.0","score":7.3,"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","level":"high"}],"updated_at":"2026-11-05T13:31:24.64316Z"},{"id":"UBUNTU-CVE-2026-61626","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.","status":"published","published":"2026-07-14T00:00:00Z","modified":"2026-11-05T11:46:35.849380491Z","cvss":[{"version":"4.0","score":7.3,"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","level":"high"}],"updated_at":"2026-11-05T13:30:15.321876Z"},{"id":"USN-8815-1","title":"libass vulnerabilities","description":"It was discovered that libass incorrectly handled parsing operations for\nspecific nested character strings. An attacker could use this issue to\ncause libass to crash, resulting in a denial of service, or possibly\nexecute arbitrary code. This issue only affected Ubuntu 14.04 LTS,\nUbuntu 16.04 LTS, Ubuntu 18.04 LTS and Ubuntu 20.04 LTS.\n(CVE-2020-24994)\n\nIt was discovered that libass incorrectly handled certain outline\nprocessing operations. An attacker could use this issue to cause libass\nto crash, resulting in a denial of service. This issue only affected\nUbuntu 18.04 LTS and Ubuntu 20.04 LTS. (CVE-2020-26682)\n\nIt was discovered that libass incorrectly handled certain ASS subtitle\nfiles when measuring wrapped lines. An attacker could use this issue to\ncause libass to crash, resulting in a denial of service, or possibly\nexecute arbitrary code. This issue only affected Ubuntu 24.04 LTS and\nUbuntu 26.04 LTS. (CVE-2026-61627)\n\nIt was discovered that libass incorrectly handled certain Matroska\nsubtitle chunks with negative ReadOrder values. An attacker could use\nthis issue to cause libass to crash, resulting in a denial of service,\nor possibly execute arbitrary code. This issue only affected Ubuntu\n26.04 LTS. (CVE-2026-61626)","status":"published","published":"2026-09-24T14:57:46Z","modified":"2026-11-03T21:18:32.82470971Z","updated_at":"2026-11-03T21:43:43.010304Z"}]}}