CVE-2026-5393 Overview
CVE-2026-5393 is an out-of-bounds read vulnerability in wolfSSL that occurs during the processing of dual-algorithm CertificateVerify messages. When handling crafted input, the library can read memory beyond the intended buffer boundaries, potentially leading to information disclosure or application instability. This vulnerability specifically affects wolfSSL builds configured with experimental dual-algorithm certificate support (--enable-experimental and --enable-dual-alg-certs build flags).
Critical Impact
Attackers with network access can exploit this vulnerability by sending maliciously crafted CertificateVerify messages, potentially causing information leakage or denial of service in TLS implementations using affected wolfSSL configurations.
Affected Products
- wolfSSL (when built with --enable-experimental flag)
- wolfSSL (when built with --enable-dual-alg-certs flag)
- Applications utilizing wolfSSL with dual-algorithm certificate functionality enabled
Discovery Timeline
- 2026-04-10 - CVE-2026-5393 published to NVD
- 2026-04-13 - Last updated in NVD database
Technical Details for CVE-2026-5393
Vulnerability Analysis
This vulnerability is classified as CWE-125 (Out-of-bounds Read), affecting wolfSSL's handling of dual-algorithm CertificateVerify messages during TLS handshakes. The dual-algorithm certificate feature is designed to support post-quantum cryptographic transitions by allowing certificates to contain multiple signature algorithms simultaneously. However, when processing specially crafted CertificateVerify messages, the parsing logic fails to properly validate buffer boundaries, resulting in an out-of-bounds memory read.
The impact is limited due to the experimental nature of the affected feature. Only wolfSSL installations explicitly compiled with both --enable-experimental and --enable-dual-alg-certs build options are susceptible. Standard production builds of wolfSSL that do not enable these experimental flags are not affected by this vulnerability.
Root Cause
The root cause stems from insufficient bounds checking in the CertificateVerify message parsing routine when dual-algorithm certificate support is enabled. During the processing of the secondary algorithm's signature data within the CertificateVerify structure, the code fails to properly validate that the message length accommodates all expected fields. This allows an attacker to craft a message that causes the parser to read beyond the allocated buffer, potentially exposing adjacent memory contents or triggering application crashes.
Attack Vector
The attack requires network access to a target service using wolfSSL with dual-algorithm certificate support enabled. An attacker can exploit this vulnerability by initiating a TLS handshake and providing a maliciously crafted CertificateVerify message during the client authentication phase. The crafted message contains manipulated length fields that cause the parser to read beyond the intended memory boundaries.
The vulnerability mechanism involves improper validation of the CertificateVerify message structure when processing dual-algorithm signatures. When the parser encounters the crafted message, it trusts the supplied length indicators without adequate bounds checking, leading to out-of-bounds memory access. For technical details on the fix, see the wolfSSL GitHub Pull Request.
Detection Methods for CVE-2026-5393
Indicators of Compromise
- Unusual TLS handshake failures or crashes in applications using wolfSSL with dual-algorithm certificates
- Application crashes with memory access violation errors during client certificate authentication
- Abnormal memory patterns or unexpected process terminations in wolfSSL-dependent services
Detection Strategies
- Monitor for TLS handshake anomalies, particularly malformed CertificateVerify messages with inconsistent length fields
- Implement application crash monitoring for wolfSSL-based services to detect potential exploitation attempts
- Deploy network intrusion detection rules to identify malformed TLS handshake packets targeting dual-algorithm certificate functionality
Monitoring Recommendations
- Enable detailed TLS handshake logging in wolfSSL-based applications to capture malformed message attempts
- Set up alerting for repeated TLS handshake failures from single source IPs that may indicate scanning or exploitation attempts
- Monitor system logs for segmentation faults or memory access errors in processes using wolfSSL libraries
How to Mitigate CVE-2026-5393
Immediate Actions Required
- Identify all wolfSSL deployments compiled with --enable-experimental and --enable-dual-alg-certs build flags
- If dual-algorithm certificate support is not required, recompile wolfSSL without the experimental flags to eliminate the vulnerability
- Apply the security patch from the wolfSSL project as detailed in Pull Request #10079
Patch Information
The wolfSSL project has addressed this vulnerability in Pull Request #10079. Organizations using wolfSSL with experimental dual-algorithm certificate support should review this patch and update their wolfSSL installations accordingly. The fix implements proper bounds checking in the CertificateVerify message parsing logic to prevent out-of-bounds reads.
Workarounds
- Disable experimental dual-algorithm certificate support by rebuilding wolfSSL without --enable-experimental and --enable-dual-alg-certs flags
- Implement network-level filtering to restrict TLS client authentication to trusted sources only
- Consider using mutual TLS authentication only from pre-approved clients until the patch can be applied
# Rebuild wolfSSL without experimental dual-algorithm certificate support
./configure --disable-experimental
make clean
make
make install
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