CVE-2026-2646 in wolfSSL
Summary
by MITRE • 03/19/2026
A heap-buffer-overflow vulnerability exists in wolfSSL's wolfSSL_d2i_SSL_SESSION() function. When deserializing session data with SESSION_CERTS enabled, certificate and session id lengths are read from an untrusted input without bounds validation, allowing an attacker to overflow fixed-size buffers and corrupt heap memory. A maliciously crafted session would need to be loaded from an external source to trigger this vulnerability. Internal sessions were not vulnerable.
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Analysis
by VulDB Data Team • 05/05/2026
The heap-buffer-overflow vulnerability identified in CVE-2026-2646 represents a critical security flaw within wolfSSL's SSL/TLS implementation that specifically affects the wolfSSL_d2i_SSL_SESSION() function. This vulnerability stems from insufficient input validation during the deserialization process of SSL session data, creating a pathway for attackers to manipulate heap memory through carefully crafted malicious inputs. The issue manifests when SESSION_CERTS functionality is enabled, which allows for certificate and session id length information to be read directly from untrusted external sources without proper bounds checking mechanisms.
The technical exploitation of this vulnerability occurs during the deserialization phase of SSL sessions where wolfSSL attempts to reconstruct session state information from previously serialized data. When SESSION_CERTS is enabled, the function reads certificate and session id length values from the input stream without validating whether these values exceed the allocated buffer boundaries. This lack of bounds validation creates a classic heap-buffer-overflow condition where attacker-controlled data can overwrite adjacent heap memory regions, potentially leading to arbitrary code execution or denial of service conditions. The vulnerability requires an external malicious session file to be loaded into the application, as internal session handling was not affected by this particular flaw.
The operational impact of CVE-2026-2646 extends beyond simple memory corruption, as it provides potential attackers with means to compromise the integrity and availability of systems relying on wolfSSL for secure communications. The heap memory corruption can result in unpredictable application behavior, crashes, or more severe exploitation scenarios where attackers might leverage the overflow to execute arbitrary code within the context of the vulnerable application. This vulnerability particularly affects applications that deserialize SSL session data from external sources, such as session caches, backup files, or network communications where session resumption is utilized. The attack vector requires an attacker to have control over the session data being loaded, making it less likely to occur in environments with proper input sanitization but still represents a significant risk in scenarios where external session data is processed.
Mitigation strategies for this vulnerability should focus on immediate patching of affected wolfSSL versions while implementing additional defensive measures. Organizations should prioritize updating to wolfSSL releases that contain fixes for this heap-buffer-overflow condition, as these updates typically include proper bounds checking and input validation for session data deserialization. Network administrators should also consider implementing strict input validation policies for any SSL session data processing, particularly when dealing with external sources or untrusted session caches. The vulnerability aligns with CWE-121 heap-based buffer overflow weakness and could potentially map to ATT&CK technique T1059.007 for code execution through memory corruption, though the specific attack surface requires proper session data manipulation to achieve successful exploitation. Additionally, deployment of runtime protections such as heap canaries or address space layout randomization may provide additional defense-in-depth measures against potential exploitation attempts.