ClamAV: Heap-based Buffer Overflow
CVE-2025-20260 is a critical-severity heap-based buffer overflow vulnerability in ClamAV from Cisco, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected ClamAV versions: 1.4.2; 1.4.1; 1.4.0, and others listed below. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 1.7% chance of exploitation within 30 days, higher than 78% of scored CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Check which version of ClamAV you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on blog.clamav.net for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Cisco | ClamAV | 1.4.2; 1.4.1; 1.4.0; 1.3.2; 1.3.1; 1.3.0; 1.2.3; 1.2.2; and 2 more ranges | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by CNA (cisco.com).
Official description
A vulnerability in the PDF scanning processes of ClamAV could allow an unauthenticated, remote attacker to cause a buffer overflow condition, cause a denial of service (DoS) condition, or execute arbitrary code on an affected device. This vulnerability exists because memory buffers are allocated incorrectly when PDF files are processed. An attacker could exploit this vulnerability by submitting a crafted PDF file to be scanned by ClamAV on an affected device. A successful exploit could allow the attacker to trigger a buffer overflow, likely resulting in the termination of the ClamAV scanning process and a DoS condition on the affected software. Although unproven, there is also a possibility that an attacker could leverage the buffer overflow to execute arbitrary code with the privileges of the ClamAV process.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Heap-based Buffer Overflow
The product writes past the end of a buffer that was allocated on the heap.
How developers prevent this class of flaw
- Pre-design: Use a language or compiler that performs automatic bounds checking.
- Use an abstraction library to abstract away risky APIs. Not a complete solution.
- Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking. D3-SFCV (Stack Frame Canary Validation) from D3FEND discusses canary-based detection in detail.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Other references
Other vulnerabilities in ClamAV
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
Recent Heap-based Buffer Overflow vulnerabilities
- 8.4 High severity
- 9.8 Critical severity
- 7.8 High severity
- 7.8 High severity
- 8.8 High severity
- 8.6 High severity
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