CVE-2025-67896
Published: 14 December 2025
Description
Exim before 4.99.1, with certain non-default rate-limit configurations, allows a remote heap-based buffer overflow because database records are cast directly to internal structures without validation.
Mitigating Controls (NIST 800-53 r5)AI
Directly mitigates the vulnerability by requiring timely patching and upgrading Exim to version 4.99.1 to remediate the heap-based buffer overflow.
Implements memory protections such as address space layout randomization and heap guards to prevent exploitation of the heap-based buffer overflow even if unpatched.
Requires validation of database records before casting to internal structures, directly addressing the lack of input validation causing the buffer overflow.
Security SummaryAI
CVE-2025-67896 is a heap-based buffer overflow vulnerability (CWE-122) affecting Exim mail transfer agent versions prior to 4.99.1. The issue arises under certain non-default rate-limit configurations, where database records are cast directly to internal structures without proper validation, enabling a remote heap-based buffer overflow. The vulnerability carries a CVSS v3.1 base score of 7.0 (AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:L), indicating high severity with network accessibility but elevated attack complexity.
Remote, unauthenticated attackers can exploit this vulnerability over the network without user interaction. Successful exploitation requires satisfying the high attack complexity, likely tied to the specific non-default rate-limit setups, and could result in low confidentiality impact (limited data exposure), high integrity impact (potential for code execution or data tampering), and low availability impact (partial denial of service).
Advisories recommend upgrading to Exim 4.99.1 to mitigate the vulnerability. Detailed reports and discussions are available in the Exim security page at https://exim.org/static/doc/security/, the specific advisory at https://exim.org/static/doc/security/EXIM-Security-2025-12-09.1/report.txt, and oss-security mailing list threads at https://www.openwall.com/lists/oss-security/2025/12/11/2, http://www.openwall.com/lists/oss-security/2025/12/14/1, and http://www.openwall.com/lists/oss-security/2025/12/18/3.
Details
- CWE(s)
Affected Products
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
CVE-2025-67896 is a remote heap-based buffer overflow in the public-facing Exim mail transfer agent, enabling unauthenticated attackers to achieve code execution, directly mapping to T1190: Exploit Public-Facing Application.