CVE-2026-6679 in wolfSSL
Summary
by MITRE • 06/26/2026
A heap buffer overflow could occur in the DTLS 1.3 ACK serialization path before the connecting peer is authenticated. The buffer overflow was due to an integer truncation when computing the length of the ACK record-number list, causing an undersized buffer to be allocated and then overrun. This affects builds using DTLS 1.3 and wolfSSL version 5.9.0 and earlier. A fix was added to the 5.9.1 release.
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Analysis
by VulDB Data Team • 06/26/2026
This vulnerability represents a critical heap buffer overflow condition that emerged in the dtls 1 3 implementation within wolfssl software libraries. The flaw manifests specifically during the acknowledgment serialization process when establishing secure connections through dtls protocol version 1 3. The issue occurs before peer authentication is completed, making it particularly dangerous as attackers could potentially exploit this weakness during the initial handshake phase of communication establishment. The vulnerability affects all implementations utilizing wolfssl versions 5 9 0 and earlier, indicating a widespread exposure across various applications and systems that depend on this cryptographic library for secure communications.
The technical root cause of this vulnerability stems from improper integer handling during the calculation of acknowledgment record-number list length. During dtls 1 3 communication setup, when constructing ack records for packet acknowledgment, the system performs integer truncation operations that result in incorrect length computations. This mathematical error leads to the allocation of insufficiently sized memory buffers that cannot accommodate the actual data requirements. When the system attempts to write acknowledgment data into these undersized buffers, it overflows the allocated memory space, potentially causing arbitrary code execution or system crashes. This type of vulnerability aligns with common weakness enumeration cw 129 which specifically addresses buffer overflow conditions due to insufficient bounds checking or incorrect size calculations.
The operational impact of this vulnerability extends beyond simple denial of service scenarios to encompass potential remote code execution capabilities. Attackers could exploit this condition by crafting malicious dtls 1 3 handshake messages that trigger the vulnerable code path during connection establishment. Since the flaw occurs before peer authentication, adversaries do not need to establish a valid secure session to exploit it, making it particularly attractive for network-level attacks. Systems running affected wolfssl versions are at risk of complete compromise if attackers successfully leverage this vulnerability to execute malicious code within the application context. The timing of the overflow during the initial handshake process means that even legitimate users could be affected by connection disruption or data corruption.
Mitigation strategies for this vulnerability require immediate software updates to wolfssl version 5 9 1 or later, which contains the necessary patches to address the integer truncation issue in ack record number list computation. Organizations should prioritize rolling out these updates across all systems utilizing dtls 1 3 functionality, particularly those handling sensitive communications or serving critical infrastructure roles. Security teams should also implement network monitoring to detect potential exploitation attempts through anomalous dtls handshake patterns that might indicate active attacks against this vulnerability. Additional defensive measures include implementing proper input validation for dtls message processing and establishing robust logging mechanisms to track connection establishment failures that could indicate exploitation attempts. The fix implemented in version 5 9 1 addresses the core integer truncation problem by ensuring correct buffer size calculations during ack record serialization, thereby preventing the memory corruption scenario that led to the vulnerability. This remediation aligns with established security practices for preventing heap-based buffer overflows and demonstrates the importance of proper integer handling in cryptographic protocol implementations.