libass up to 0.17.4 Line Measurement wrap_lines_measure buffer overflow

Summaryinfo

A vulnerability was found in libass up to 0.17.4 and classified as problematic. The affected element is the function wrap_lines_measure of the component Line Measurement. Executing a manipulation can lead to buffer overflow. This vulnerability is registered as CVE-2026-61627. It is possible to launch the attack remotely. No exploit is available. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability has been found in libass up to 0.17.4 and classified as problematic. This vulnerability affects the function wrap_lines_measure of the component Line Measurement. The manipulation with an unknown input leads to a buffer overflow vulnerability. The CWE definition for the vulnerability is CWE-120. The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer, leading to a buffer overflow. As an impact it is known to affect availability. CVE summarizes:

libass is a portable subtitle renderer for the `ASS`/SSA (Advanced Substation Alpha/Substation Alpha) subtitle format. Prior to 0.17.5, libass can overread and overwrite the glyph array in `wrap_lines_measure` while rendering malicious `ASS` content. In `wrap modes other than two`, a final line ending with a literal backslash-n sequence and otherwise consisting only of such sequences or spaces can remain after early trimming and make the line-measurement loops overshoot by one glyph. When the total text size exactly matches the allocated glyph-array capacity, the first loop reads an uninitialized 32-bit fixed-point `pos.x` value, although that value is not subsequently used. The second loop writes `pos.x` and `pos.y` beyond the array, zeroing the first and adding an attacker-controllable offset to the second. No actual exploitation beyond possible denial of service is known; broader exploitation is theoretical and constrained by the addresses, limited writes, and ASLR. This issue is fixed in version 0.17.5.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-61627 since 07/10/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Successful exploitation requires user interaction by the victim. There are known technical details, but no exploit is available.

Upgrading to version 0.17.5 eliminates this vulnerability.

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Productinfo

Name

• libass

Version

• 0.17.0
• 0.17.1
• 0.17.2
• 0.17.3
• 0.17.4

Website

• Product: https://github.com/libass/libass/

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