CVE-2026-61626: Memory Corruption

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.

Is your site exposed to CVE-2026-61626?

Run a free security scan — no signup, results in seconds.

Weakness Type (CWE)

CWE-787 Out-of-bounds Write

References

Other References

https://github.com/libass/libass/commit/23da65a130bb8c5b2cf0c7df0dd7d424607f98f1 https://github.com/libass/libass/releases/tag/0.17.5 https://github.com/libass/libass/security/advisories/GHSA-5gf7-wjfm-vmvm

Frequently Asked Questions

What is CVE-2026-61626? +

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.

How do I check if I'm vulnerable to CVE-2026-61626? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

CVE-2026-8358

LibreOffice Calc can import tracked changes from a spreadsheet document. A heap buffer overflow existed when a document reused the …

CVE-2026-8356

LibreOffice can import presentations in the legacy binary PPT format. A stack buffer overflow existed when importing a colour-replacement record. …

CVE-2026-6040

A heap use-after-free existed when importing the blank-width characters of an ODF number format. A position value read from the …

CVE-2026-6039

LibreOffice can import drawings in the DXF format used by CAD software. A heap buffer overflow existed when importing a …

CVE-2026-3298

The method "sock_recvfrom_into()" of "asyncio.ProacterEventLoop" (Windows only) was missing a boundary check for the data buffer when using nbytes parameter. …

CVE-2026-40489

editorconfig-core-c is an EditorConfig core library for use by plugins supporting EditorConfig parsing. Versions up to and including 0.12.10 have …

CVE-2026-61626