Raw vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:LSummary
CVE-2025-67896 is a high-severity Heap-based Buffer Overflow (CWE-122) vulnerability in Exim Exim. Its CVSS base score is 7.0 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 38th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SI-10 (Information Input Validation) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
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.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2025-203281
Vulnerability Data
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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V1.4.1
Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation (including fuzzing and memory-error detectors) can discover heap overflows after they have been coded.
Input validation enforces bounds checking on data written to heap buffers, directly stopping the overflow condition from being introduced.
Security engineering principles require use of memory-safe constructs and bounds-checked allocation routines that avoid introducing heap overflows.
Memory-protection mechanisms limit the ability of a heap overflow to execute attacker-controlled code or corrupt adjacent structures.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure-development practices directly require bounds checking and safe memory handling that prevent heap overflows.
Vulnerability scanning and recording can discover heap-overflow flaws but does not prevent their introduction in code.
Timely patching removes known heap-overflow instances after they exist.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing in development and acceptance can detect heap overflows before release.
Secure development lifecycle mandates practices that reduce the likelihood of introducing heap overflows.
Application security requirements can specify bounds-checking and safe memory APIs that mitigate heap overflows.
Secure architecture and engineering principles include memory-safety and input-validation controls that address heap overflows.
Secure coding standards directly prescribe techniques (safe functions, bounds checks) that prevent heap-based buffer overflows.
Change management ensures controlled deployment of fixes for discovered heap-overflow vulnerabilities.