Aegisub EUVD-2026-95988

Exploitation requires the victim to open, within Aegisub 3.2.0-3.4.2, a crafted .ass subtitle project whose 'Automation Scripts' metadata references an attacker-supplied Lua Automation script; Aegisub auto-loads that script without any trust/authorship confirmation. The attacker must get both the ASS file and the referenced script to the victim (e.g., distributed together), except on 3.4.0-3.4.2 where inconsistent handling of embedded NUL characters between extension validation and filesystem operations lets a single crafted ASS/Lua polyglot reference and execute itself, removing the need for a separate script file. Limiting factors: the vector is local (AV:L) and requires user interaction (UI:R) to open the file, it does not affect default behavior of any network service, and only versions 3.2.0 through 3.4.2 are affected (fixed in 3.5.0).

This is a genuine code-execution flaw but its real-world urgency is moderate, not critical. The CVSS 3.1 vector (AV:L/AC:L/PR:N/UI:R) correctly models a social-engineering file-open attack rather than a remotely reachable service bug: the attacker cannot reach a victim over the network and instead must convince the user to open a malicious ASS subtitle project (UI:R), which then auto-loads a referenced Lua Automation script with full code execution (C:H/I:H/A:H). The 7.8 'High' score is driven almost entirely by the triple-high impact, while the local vector and required user interaction meaningfully cap exploitability. No EPSS score, CISA KEV listing, or public POC is present in the supplied data, so there is no public exploit identified at time of analysis and no evidence of active or widespread exploitation - the risk is latent and depends on tricking a specific user. The vulnerability is credibly confirmed by the vendor's own GitHub Security Advisory (GHSA-67hq-5vgg-6f23) and three linked remediation commits, so the technical validity is high even though threat-intel exploitation signals are absent. Net: treat as a priority for the Aegisub user community (particularly fansub/typesetting workflows where ASS files are routinely exchanged), but it is not an internet-facing emergency.

An attacker publishes or shares a seemingly legitimate .ass subtitle project (e.g., on a fansub forum or download site) bundled with a malicious Lua Automation script it references, or on 3.4.0-3.4.2 a single ASS/Lua polyglot using an embedded NUL to self-reference. When the victim opens the file in a vulnerable Aegisub (3.2.0-3.4.2), the script is loaded automatically with no trust prompt and runs arbitrary code at the privileges of the Aegisub process. No public exploit code is identified in the provided data, but the attack requires only standard file-sharing and the victim opening the file.