CVE-2026-5392: PKCS7 Parsing Buffer Overflow Vulnerability

CVE-2026-5392 Overview

A heap out-of-bounds read vulnerability exists in the PKCS7 parsing functionality. A specially crafted PKCS7 message can trigger an out-of-bounds read on the heap due to a missing bounds check in the indefinite-length end-of-content verification loop within the PKCS7_VerifySignedData() function.

Critical Impact

An attacker on an adjacent network could potentially exploit this vulnerability to read sensitive heap memory or cause application instability through crafted PKCS7 messages.

Affected Products

• wolfSSL (specific versions not disclosed in CVE data)

Discovery Timeline

• April 10, 2026 - CVE CVE-2026-5392 published to NVD
• April 13, 2026 - Last updated in NVD database

Technical Details for CVE-2026-5392

Vulnerability Analysis

This vulnerability is classified as CWE-125 (Out-of-bounds Read), a memory safety issue that occurs when software reads data past the end or before the beginning of an intended buffer. In this specific case, the vulnerability resides in the PKCS7 signature verification routine.

The flaw is triggered when processing indefinite-length encoded content within PKCS7 messages. During the end-of-content verification loop in PKCS7_VerifySignedData(), the parser fails to properly validate buffer boundaries before reading heap memory, allowing an attacker to craft a malicious PKCS7 message that causes the parser to read beyond allocated memory regions.

Root Cause

The root cause is a missing bounds check in the indefinite-length end-of-content verification loop. When parsing PKCS7 structures with indefinite-length encoding, the verification function iterates through content looking for end-of-content markers but does not properly validate that read operations remain within the allocated buffer boundaries. This allows carefully crafted input to force reads outside the intended memory region.

Attack Vector

The attack requires adjacent network access, meaning the attacker must be on the same network segment as the target system. The attacker would craft a malicious PKCS7 message with specially constructed indefinite-length encoded content designed to trigger the out-of-bounds read condition. When the vulnerable PKCS7_VerifySignedData() function processes this message, it reads heap memory beyond the intended buffer boundaries.

The vulnerability manifests in the boundary checking logic within the PKCS7 parsing routine. Technical details and the fix can be found in the wolfSSL GitHub Pull Request #10039.

Detection Methods for CVE-2026-5392

Indicators of Compromise

• Unexpected application crashes or segmentation faults during PKCS7 signature verification operations
• Abnormal memory access patterns detected by memory sanitizers (ASan/MSan) in applications using wolfSSL
• Unusual PKCS7 messages with malformed indefinite-length encoding in network traffic

Detection Strategies

• Deploy application-level monitoring for crashes in wolfSSL-dependent services, particularly those handling PKCS7 content
• Utilize AddressSanitizer (ASan) in development and testing environments to detect out-of-bounds read attempts
• Monitor for anomalous PKCS7 message structures at network ingress points

Monitoring Recommendations

• Enable verbose logging for cryptographic operations in affected applications
• Implement network traffic analysis for malformed ASN.1/PKCS7 structures
• Configure crash reporting and analysis for applications utilizing wolfSSL cryptographic functions

How to Mitigate CVE-2026-5392

Immediate Actions Required

• Review applications and systems that utilize wolfSSL for PKCS7 parsing functionality
• Apply the security patch from the wolfSSL repository when available
• Consider temporarily disabling PKCS7 signature verification functionality in high-risk environments until patched

Patch Information

A fix has been developed and is available via wolfSSL GitHub Pull Request #10039. Organizations should review this pull request and apply the updated wolfSSL version containing the fix to affected systems. The patch adds proper bounds checking to the indefinite-length end-of-content verification loop in PKCS7_VerifySignedData().

Workarounds

• Restrict network access to systems processing PKCS7 content to trusted sources only
• Implement input validation and filtering for PKCS7 messages before passing to wolfSSL functions
• Consider using network segmentation to limit adjacent network attack surface

# Configuration example
# Limit network access to systems with wolfSSL PKCS7 functionality
# Example iptables rule to restrict access to trusted networks only
iptables -A INPUT -s 192.168.1.0/24 -p tcp --dport 443 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP