CVE-2026-7531 in wolfSSL
Summary
by MITRE • 06/25/2026
Use-after-free in PQC hybrid key-share handling. This is an incomplete-fix follow-up to CVE-2026-5460 (released in 5.9.1): a malicious TLS 1.3 server sending a truncated PQC hybrid KeyShare can still trigger the error cleanup path to operate on freed memory.
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Analysis
by VulDB Data Team • 06/26/2026
This vulnerability represents a critical use-after-free condition in the handling of post-quantum cryptography hybrid key shares within TLS 1.3 implementations. The flaw manifests when a malicious server sends a truncated post-quantum cryptography hybrid KeyShare during the TLS handshake process, which triggers an error cleanup routine that operates on memory that has already been freed. This represents an incomplete remediation of a previously identified vulnerability CVE-2026-5460, which was addressed in version 5.9.1 of the affected software. The vulnerability falls under CWE-416, which specifically addresses use-after-free conditions where memory is accessed after it has been freed, and aligns with ATT&CK technique T1190 for exploitation through vulnerabilities in cryptographic libraries. The issue occurs during the TLS 1.3 handshake when the client processes key shares from a malicious server, creating a scenario where the error handling codepath attempts to access memory structures that have already been deallocated.
The technical implementation of this vulnerability exploits the inherent complexity of hybrid cryptographic key exchange mechanisms that combine traditional and post-quantum cryptographic algorithms. In TLS 1.3, when a client receives a KeyShare from a server, it must validate the structure and contents of these shares before proceeding with the handshake. The specific flaw occurs when a malicious server sends a truncated PQC hybrid KeyShare that does not conform to expected format specifications. This triggers an early termination of the key share processing, which should normally result in proper cleanup of allocated resources. However, due to incomplete error handling logic, the code attempts to access freed memory structures during the cleanup phase, leading to potential memory corruption and undefined behavior.
The operational impact of this vulnerability extends beyond simple memory corruption as it provides a potential attack vector for remote code execution or denial-of-service conditions. When exploited, this use-after-free condition can lead to system instability, application crashes, or in some cases, allow attackers to execute arbitrary code on the affected system. The vulnerability is particularly concerning in environments where TLS 1.3 is extensively used for secure communications, including web servers, email systems, and other network services that rely heavily on proper cryptographic handshake processing. The fact that this represents a follow-up issue from CVE-2026-5460 indicates that the initial patch was insufficient to address all code paths that could lead to memory access violations during error conditions.
Mitigation strategies for this vulnerability should focus on implementing comprehensive memory management practices and robust error handling procedures within TLS implementations. Organizations should prioritize upgrading to patched versions of their cryptographic libraries, ensuring that all error cleanup paths properly handle freed memory references and implement proper null checks before accessing memory structures. Additional protective measures include deploying network monitoring solutions that can detect anomalous KeyShare patterns from malicious servers, implementing strict validation controls for incoming TLS handshake messages, and considering the use of intrusion detection systems that can identify potential exploitation attempts. The fix should ensure that all memory allocated during key share processing is properly tracked and that cleanup routines only access valid memory regions, preventing any scenario where freed memory might be accessed during error handling operations.