# CVE-2025-11187: OpenSSL mishandles PBMAC1 parameters in PKCS#12

- **Published on:** 2026-01-27
- **Category:** Security
- **Original page:** https://linuxgratis.com/en/articles/cve-2025-11187-openssl-pkcs12-pbmac1

OpenSSL fixes a flaw in the MAC verification of PBMAC1-protected PKCS#12 files that can cause a stack buffer overflow or denial of service. Affected versions, severity and patches.

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On 27 January 2026 the OpenSSL project published a security advisory for **CVE-2025-11187**, a **moderate-severity** vulnerability in how the library processes **PKCS#12** files protected with **PBMAC1**. The flaw comes down to missing validation of **PBKDF2** parameters during MAC (Message Authentication Code) verification, which can crash the application and cause a **denial of service (DoS)**.

## What the vulnerability is

PKCS#12 files (`.p12` or `.pfx` extensions) are containers that usually store private keys, certificates and trust chains. They embed a MAC to protect their integrity. When that MAC is computed with **PBMAC1** —a more modern scheme that derives the key with PBKDF2— OpenSSL failed to properly validate two parameters that the file itself controls:

- **The PBKDF2 key length (keylength).** If the declared value exceeds the 64-byte stack buffer reserved for the derivation, a **stack buffer overflow** occurs.
- **The salt type.** An invalid salt type leads to the use of an **invalid pointer** or a **NULL pointer dereference**.

In practice, what OpenSSL describes is a **crash of the process** that parses an untrusted PKCS#12 file.

## Who is affected and severity

The affected branches are **OpenSSL 3.6, 3.5 and 3.4**. The problem only shows up when an application processes a **malicious or crafted** PKCS#12 file.

OpenSSL rated the flaw as **moderate** rather than high for a clear reason: PKCS#12 files almost always contain **trusted private keys** that the user or system generated or imported, so they rarely count as untrusted external input. The real risk sits with services that accept and parse PKCS#12 files supplied by third parties, such as certificate upload portals or automated import systems. There, an attacker could send a `.p12` crafted to crash the service.

The advisory mentions the potential for a stack buffer overflow, but OpenSSL keeps the realistic impact at **denial of service**, with no confirmed code execution.

## Mitigation and patches

The fix is already available in these versions, which you should upgrade to:

- **OpenSSL 3.6.1**
- **OpenSSL 3.5.5**
- **OpenSSL 3.4.4**

Linux distributions have been shipping their own fixed packages: **Debian** handled it in advisory **DSA-6113-1** and **Red Hat** in **RHSA-2026:1496**. The sensible move is to apply the update through your distribution's package manager (`apt`, `dnf`, etc.) instead of building OpenSSL by hand, since that also updates the linked binaries and base-system libraries.

Until the patch is in place, avoid processing PKCS#12 files of unknown origin and, in services that accept them, validate and isolate that input flow.

## Source

- OpenSSL Security Advisory (20260127): [https://openssl-library.org/news/secadv/20260127.txt](https://openssl-library.org/news/secadv/20260127.txt)
- Vulnerability detail on NVD: [https://nvd.nist.gov/vuln/detail/CVE-2025-11187](https://nvd.nist.gov/vuln/detail/CVE-2025-11187)