CVE-2025-11187: OpenSSL Buffer Overflow Vulnerability

CVE-2025-11187 Overview

CVE-2025-11187 is a vulnerability in OpenSSL affecting PBMAC1 parameter validation in PKCS#12 files. The flaw can trigger a stack-based buffer overflow, invalid pointer, or NULL pointer dereference during MAC verification when processing maliciously crafted PKCS#12 files.

The vulnerability occurs because PBKDF2 salt and keylength parameters from PKCS#12 files using PBMAC1 for MAC verification are used without proper validation. When the keylength value exceeds the 64-byte fixed stack buffer used for the derived key, a buffer overflow occurs with attacker-controlled length. Additionally, if the salt parameter is not an OCTET STRING type, this can lead to invalid or NULL pointer dereference conditions.

Critical Impact

This vulnerability may cause a crash leading to Denial of Service for applications that parse untrusted PKCS#12 files. The buffer overflow may also potentially enable code execution depending on platform mitigations.

Affected Products

• OpenSSL 3.6
• OpenSSL 3.5
• OpenSSL 3.4

Discovery Timeline

• 2026-01-27 - CVE CVE-2025-11187 published to NVD
• 2026-01-29 - Last updated in NVD database

Technical Details for CVE-2025-11187

Vulnerability Analysis

This vulnerability represents a classic case of insufficient input validation in cryptographic library functions. The PBMAC1 (Password-Based Message Authentication Code 1) implementation in OpenSSL fails to validate user-controllable parameters before using them in security-critical operations.

The core issue lies in the PKCS#12 MAC verification process. When a PKCS#12 file specifies PBMAC1 as the MAC algorithm, OpenSSL reads the PBKDF2 (Password-Based Key Derivation Function 2) parameters directly from the file structure without bounds checking. The keylength parameter is particularly dangerous as it directly controls how many bytes are written to a fixed 64-byte stack buffer during key derivation.

The NULL pointer dereference variant occurs when the salt parameter has an unexpected ASN.1 type. The code expects an OCTET STRING type but does not properly validate this, leading to pointer issues when processing malformed data.

Root Cause

The root cause is missing validation of PBMAC1 parameters in PKCS#12 file parsing. Specifically, the PBKDF2 keylength parameter is not validated against the 64-byte stack buffer size before key derivation, and the salt parameter type is not verified to be an OCTET STRING before dereferencing.

Attack Vector

Exploitation requires an attacker to craft a malicious PKCS#12 file with manipulated PBMAC1 parameters. The attack vector is local, requiring the victim to open or process the malicious file through an application using vulnerable OpenSSL versions.

The attack scenario involves:

1. Creating a PKCS#12 file that uses PBMAC1 for MAC
2. Setting the keylength parameter to a value greater than 64 bytes to trigger the buffer overflow
3. Alternatively, setting the salt parameter to a non-OCTET STRING type to trigger pointer issues
4. Convincing a user or application to process the malicious file

While exploiting this issue requires processing a maliciously crafted PKCS#12 file, the practical exploitability is limited because it is uncommon for applications to accept untrusted PKCS#12 files. These files are typically used to store private keys which are trusted by definition. For this reason, the OpenSSL project assessed this as moderate severity.

It should be noted that the FIPS modules in versions 3.6, 3.5, and 3.4 are not affected by this issue, as PKCS#12 processing is outside the OpenSSL FIPS module boundary. OpenSSL versions 3.3, 3.0, 1.1.1, and 1.0.2 are not affected as they do not support PBMAC1 in PKCS#12.

Detection Methods for CVE-2025-11187

Indicators of Compromise

• Unexpected application crashes when processing PKCS#12 files
• Stack corruption or segmentation faults in processes using OpenSSL for certificate handling
• Anomalous PKCS#12 files with unusually large keylength values in PBMAC1 parameters
• Memory corruption indicators in application logs during certificate import operations

Detection Strategies

• Monitor for crashes in applications that process PKCS#12 files, particularly with stack-based crash signatures
• Implement file integrity monitoring on systems that regularly process certificate files
• Use static analysis tools to identify applications using vulnerable OpenSSL versions for PKCS#12 processing
• Deploy endpoint detection capabilities to identify exploitation attempts through abnormal memory access patterns

Monitoring Recommendations

• Enable detailed logging for certificate processing operations in affected applications
• Monitor for unusual PKCS#12 file submissions to certificate management systems
• Implement alerting for application crashes with stack overflow signatures
• Track OpenSSL version usage across your infrastructure to identify vulnerable deployments

How to Mitigate CVE-2025-11187

Immediate Actions Required

• Upgrade OpenSSL to patched versions as soon as they become available
• Audit applications that process PKCS#12 files from potentially untrusted sources
• Implement strict input validation for any PKCS#12 file processing workflows
• Consider restricting PKCS#12 file imports to trusted sources only until patches are applied

Patch Information

OpenSSL has released security patches to address this vulnerability. The fixes add proper validation of PBMAC1 parameters before use. Security patches are available via the following commits:

• GitHub OpenSSL Commit 205e3a5
• GitHub OpenSSL Commit 8caf359
• GitHub OpenSSL Commit e1079bc

For complete details, refer to the OpenSSL Security Advisory.

Workarounds

• Restrict PKCS#12 file processing to trusted sources only
• Implement application-level input validation to reject PKCS#12 files with suspicious parameters
• If possible, downgrade to OpenSSL 3.3 or earlier which do not support PBMAC1 in PKCS#12
• Isolate certificate processing operations in sandboxed environments to limit potential impact

# Check OpenSSL version to determine vulnerability status
openssl version -a

# Verify if PBMAC1 support is present (affected versions only)
# Affected: OpenSSL 3.4, 3.5, 3.6
# Not affected: OpenSSL 3.3, 3.0, 1.1.1, 1.0.2