CVE-2025-53816 is a heap-based buffer overflow vulnerability identified in the RAR5 archive handler component of the 7-Zip file archiver, specifically in versions prior to 25.0.0. The vulnerability arises because the software writes zero bytes outside the bounds of the allocated heap buffer during the processing of RAR5 archives. This out-of-bounds write leads to memory corruption, which can cause the application to crash or behave unpredictably, resulting in a denial of service (DoS) condition. The flaw does not require any user interaction, elevated privileges, or authentication, and can be triggered by simply opening or extracting a crafted malicious RAR5 archive using a vulnerable 7-Zip version. The CVSS 4.0 base score is 5.5, reflecting a medium severity level, with the attack vector being local (AV:L), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N), and a high impact on availability (VA:H). No known exploits have been reported in the wild as of the publication date, but the vulnerability poses a risk to systems that rely on 7-Zip for handling RAR5 archives. The issue has been addressed and fixed in 7-Zip version 25.0.0, which prevents zero writes outside the heap buffer, thereby eliminating the memory corruption risk.

For European organizations, this vulnerability primarily threatens the availability of systems that use vulnerable versions of 7-Zip to process RAR5 archives. A successful exploitation can cause application crashes or denial of service, potentially disrupting workflows that depend on file archiving and extraction. This could affect sectors such as finance, government, manufacturing, and critical infrastructure where 7-Zip is commonly used for data compression and decompression. Although the vulnerability does not directly compromise confidentiality or integrity, repeated crashes or service interruptions could lead to operational downtime, impacting productivity and potentially delaying critical processes. Since exploitation requires local access to process malicious archives, the risk is higher in environments where users frequently exchange or open untrusted compressed files. The absence of known exploits reduces immediate risk but does not eliminate the threat, especially in targeted attacks or insider threat scenarios.

The primary mitigation is to upgrade all instances of 7-Zip to version 25.0.0 or later, which contains the fix for this vulnerability. Organizations should implement strict policies to prevent the use of outdated 7-Zip versions, especially on endpoints that handle external or untrusted archives. Additionally, restricting the processing of RAR5 archives from untrusted sources can reduce exposure. Employ endpoint security solutions that monitor and block suspicious archive files or anomalous application crashes. Conduct user awareness training to highlight the risks of opening unknown compressed files. For environments where upgrading is delayed, consider sandboxing or isolating archive extraction processes to contain potential crashes. Regularly audit software inventories to ensure compliance with patching policies and monitor security advisories for updates on exploit developments.