Description

A vulnerability in the XAR file format parser of ClamAV could allow an unauthenticated, remote attacker to cause a DoS condition or possibly other expanded impacts as a result of memory corruption on an affected device. This vulnerability is due to improper boundary checks for content in XAR files during scanning. An attacker could exploit this vulnerability by submitting a crafted file that contains XAR content to be scanned by ClamAV on an affected device. A successful exploit could allow the attacker to cause the ClamAV scanning process to terminate, resulting in a DoS condition on the affected software.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.5",
  "pubDate": "2026-08-07T17:17:03.537Z",
  "pubdate": "2026-08-07T17:17:03.537Z",
  "executiveSummary": "A memory corruption vulnerability exists in the XAR file format parser of ClamAV, arising from improper boundary checks during the scanning of crafted files. This flaw allows an unauthenticated, remote attacker to trigger a Denial of Service (DoS) condition or potentially achieve other impacts on affected devices. The root cause stems from inadequate validation of input data lengths within the XAR parsing routines. To exploit this vulnerability, an attacker must submit a maliciously crafted XAR file to be processed by the ClamAV scanning engine. Upon successful processing, the vulnerability causes the ClamAV scanning process to crash or terminate unexpectedly, disrupting dependent security services and leaving systems temporarily or permanently unprotected. The risk implication is significant for environments relying on automated email or file gateway scanning powered by ClamAV, as a single malicious payload can interrupt core security monitoring. No authentication or elevated privileges are required to initiate the attack vector, provided the targeted system processes the untrusted input file.",
  "technicalDetails": "The vulnerability resides within the XAR file format parsing component of ClamAV, specifically in the logic responsible for handling internal file structures and metadata headers. The root cause is categorized as an improper boundary check, wherein the parser fails to adequately validate the size and offsets of incoming data streams against allocated memory buffers. When ClamAV attempts to parse a malformed or maliciously crafted XAR file submitted for scanning, the lack of rigorous bounds checking allows out-of-bounds memory operations to occur during data extraction or decompression phases. Attack flow begins when an unauthenticated remote attacker transmits or deposits a specially crafted XAR file into a context monitored or scanned by ClamAV, such as an email attachment, web upload, or shared directory. The ClamAV scanning engine ingests the file and dispatches it to the XAR parsing subsystem. As the parser reads the manipulated structural metadata within the XAR payload, it calculates incorrect memory offsets or copies excessive data into static or dynamic buffers without verifying destination capacity. This results in memory corruption, typically manifesting as a heap-based or stack-based buffer overflow, depending on the internal allocation mechanism targeted. The immediate consequence of this memory corruption is an unhandled exception or segmentation fault, causing the scanning daemon or process to terminate abnormally. Network exposure is dependent on how ClamAV is integrated into network services, but remote exploitation is feasible if public-facing mail transfer agents or web applications pass untrusted inputs directly to the scanner. Post-exploitation impact is primarily focused on achieving a Denial of Service via process termination, though theoretical memory corruption scenarios could lead to arbitrary code execution if precise memory layout manipulation is achieved by the attacker. Authentication and privilege requirements are absent, as the parsing engine processes untrusted data directly from external sources without prior session establishment."
}