CVE-2025-67896

High

Published: 14 December 2025

Published

14 December 2025

Modified

22 December 2025

KEV Added

—

Patch

—

CVSS Score 7.0 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:L

EPSS Score 0.0011 29.3th percentile

Risk Priority 14 60% EPSS · 20% KEV · 20% CVSS

Summary

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 Exploit Public-Facing Application (T1190); ranked at the 29.3th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified are NIST 800-53 SI-10 (Information Input Validation) and SI-16 (Memory Protection).

Threat & Defense at a Glance

What attackers do: exploitation maps to Exploit Public-Facing Application (T1190). What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

SI-2 Flaw Remediation good match

prevent

Directly mitigates the vulnerability by requiring timely patching and upgrading Exim to version 4.99.1 to remediate the heap-based buffer overflow.

SI-16 Memory Protection good match

prevent

Implements memory protections such as address space layout randomization and heap guards to prevent exploitation of the heap-based buffer overflow even if unpatched.

SI-10 Information Input Validation good match

prevent

Requires validation of database records before casting to internal structures, directly addressing the lack of input validation causing the buffer overflow.

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access

Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.

attack.mitre.org →

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.

Confidence: HIGH · MITRE ATT&CK Enterprise v19.0

NVD 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.

Deeper analysisAI

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.