CVE-2026-0819: 
wolfSSL vulnerability analysis and mitigation

CVE-2026-0819 is a stack-based buffer overflow vulnerability in wolfSSL's PKCS7 SignedData encoding functionality, specifically within the wc_PKCS7_BuildSignedAttributes() function. It affects wolfSSL versions 5.5.0 through 5.8.x (prior to 5.9.0). The vulnerability was published on March 19, 2026, and a fix was merged into the wolfSSL master branch on January 9, 2026 (PR #9630). It carries a CVSS v3.1 base score of 7.1 (High) and a CVSS v4.0 base score of 2.2 (Low) (Feedly, GitHub PR).

The root cause is an out-of-bounds write (CWE-787 / CWE-121) in wc_PKCS7_BuildSignedAttributes(). When adding custom signed attributes, the function incorrectly passes esd->signedAttribsCount as the capacity argument to EncodeAttributes() instead of the remaining available space in the fixed-size signedAttribs[7] array (MAX_SIGNED_ATTRIBS_SZ defaults to 7). If an application sets pkcs7->signedAttribsSz to a value exceeding MAX_SIGNED_ATTRIBS_SZ minus the number of default attributes already added, EncodeAttributes() writes beyond the array bounds, corrupting stack memory. In WOLFSSL_SMALL_STACK builds, the overflow instead corrupts heap memory. Exploitation requires an application that allows untrusted input to control the signedAttribs array size when calling wc_PKCS7_EncodeSignedData() or related signing functions (Feedly, GitHub PR).

Successful exploitation results in stack or heap memory corruption (depending on build configuration), with high integrity and availability impacts but no direct confidentiality impact. Affected applications may crash (denial of service), and in more severe scenarios, an attacker could potentially leverage the memory corruption for arbitrary code execution by overwriting critical data structures. The attack vector is local and requires low privileges (CVSS v3.1), limiting the blast radius, but embedded or IoT deployments using wolfSSL for PKCS7 operations may be particularly at risk (Feedly).

1. Identify a vulnerable target: Locate an application using wolfSSL versions 5.5.0–5.8.x that exposes PKCS7 SignedData encoding functionality (wc_PKCS7_EncodeSignedData() or related functions) and allows user-controlled input to influence the signedAttribs array size.
2. Craft malicious input: Prepare input that sets pkcs7->signedAttribsSz to a value greater than MAX_SIGNED_ATTRIBS_SZ (7) minus the number of default attributes already added by the library (typically 2–3), causing the total to exceed the fixed array bounds.
3. Trigger the overflow: Submit the crafted input through the application's interface (e.g., a file upload, API call, or local process invocation) to invoke wc_PKCS7_BuildSignedAttributes(), which passes the incorrect capacity to EncodeAttributes().
4. Achieve memory corruption: EncodeAttributes() writes beyond the signedAttribs[7] array bounds, corrupting adjacent stack memory (or heap memory in WOLFSSL_SMALL_STACK builds), potentially overwriting return addresses, function pointers, or other critical data.
5. Leverage corruption: Depending on the application and memory layout, the attacker may trigger a crash (DoS) or, with precise control over the overflow content, attempt to redirect execution flow for arbitrary code execution (Feedly, GitHub PR).

• Logs: Application crash logs or core dumps originating from wolfSSL PKCS7 encoding functions (wc_PKCS7_BuildSignedAttributes, EncodeAttributes); stack smashing detection messages (e.g., *** stack smashing detected ***) in system logs.
• Process: Unexpected application crashes or abnormal termination of processes using wolfSSL during PKCS7 signing operations; unusual child processes spawned after a PKCS7 encoding call.
• File System: Core dump files generated by applications using wolfSSL in directories with write access; unexpected binary or script files created post-crash in application working directories.
• Network: In network-exposed applications, repeated malformed PKCS7 signing requests from a single source IP, particularly with unusually large signedAttribs counts.

The primary remediation is to upgrade wolfSSL to version 5.9.0 or later, which includes the fix merged via GitHub PR #9630 on January 9, 2026. As interim workarounds: (1) review all applications using wolfSSL to identify whether untrusted input can reach PKCS7 signing functions; (2) implement strict input validation and access controls to limit which users or processes can trigger wc_PKCS7_EncodeSignedData() or related functions; (3) consider disabling PKCS7 functionality entirely if it is not required by the application. FreeBSD ports users can reference the wolfssl port update for package-level remediation (GitHub PR, Feedly).

The vulnerability received routine coverage from vulnerability tracking platforms including VulnDB, CVEFeed, and ENISA's EUVD (EUVD-2026-13131) shortly after publication. A Bluesky post from a CVE tracking account noted the disclosure. No significant vendor statements beyond the patch PR, major researcher commentary, or widespread media coverage has been observed, consistent with the vulnerability's constrained exploitation prerequisites and low EPSS score (Feedly).