Avira Antivirus EUVD-2025-210131

Exploitation requires (1) Avira Antivirus running an engine build older than 8.3.70.56 on Windows, macOS, or Linux; (2) a Windows MSI file with a specifically malformed structure delivered to a path the engine will scan; and (3) the engine actually invoking its MSI parser on that file, either via on-access scanning when the file lands on disk, scheduled/manual scans, or user-initiated 'scan this file' actions (the UI:R element of the CVSS vector). Limiting factors are that the attacker needs a delivery primitive to place the file on the target system, the bug is local (not network-reachable via the engine itself), and the malformed MSI must survive intermediate handling (mail gateways, archive extractors) intact enough for the Avira parser to dereference the out-of-bounds region.

Real-world risk is moderate-to-high but not internet-facing. The CVSS vector AV:L/AC:L/PR:N/UI:R reflects that an attacker cannot reach the engine remotely on their own: a local file (planted via download, email attachment, USB, or shared folder) must be processed by the AV engine, typically when a user interacts with it or on-access scanning fires. Triggering the bug yields C:H/I:H/A:H because the Avira engine usually runs with elevated privileges, making successful code execution effectively a local privilege escalation. There is no EPSS, KEV, or POC indication in the supplied intelligence, suggesting opportunistic mass exploitation is unlikely; however, AV engines are historically high-value targets for endpoint privilege escalation, so the risk for targeted intrusions is meaningful. The 'UI:R' requirement is conservative - on-access scanners often process files without explicit user action, so defenders should not over-discount on that basis.

An attacker emails or hosts a crafted MSI installer and induces the victim to download or open the containing folder; Avira's on-access or on-demand scan parses the malformed MSI structure and reads past the heap buffer. The resulting memory corruption either crashes the AV service (denial of service that leaves the host unprotected) or, with a tuned payload, achieves local code execution in the privileged engine context. No public exploit identified at time of analysis, but the bug class - AV-engine file-format parser - has a well-documented exploitation history.