CVE-2026-6681 in wolfSSL
Summary
by MITRE • 06/26/2026
The PKCS#7 decode path ignores the caller-supplied output buffer size (outputSz), allowing decoded content to be written past the bounds of the provided buffer. This affects wolfSSL 5.9.0 and earlier and was fixed in the 5.9.1 release.
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Analysis
by VulDB Data Team • 06/26/2026
This vulnerability resides within the cryptographic library wolfSSL and specifically impacts the PKCS#7 decoding functionality that handles secure message formatting and enveloping operations. The flaw manifests when the decode function processes incoming data without properly validating the caller-provided buffer size parameter, creating a classic buffer overflow condition. The issue affects versions 5.9.0 and earlier of the library, indicating it was present in a relatively recent release cycle where security patches should have been prioritized.
The technical implementation flaw occurs in the PKCS#7 decoding path where the function fails to enforce bounds checking against the outputSz parameter that callers provide to specify buffer capacity. When processing encoded content, the decoder writes decoded data directly to the provided buffer without verifying that the destination can accommodate the full output size. This oversight allows maliciously crafted PKCS#7 structures to cause memory corruption by writing beyond allocated buffer boundaries, potentially leading to arbitrary code execution or denial of service conditions.
Operationally, this vulnerability presents significant risks in environments where wolfSSL handles untrusted PKCS#7 encoded data such as certificate chains, signed messages, or encrypted content. Attackers could exploit this by crafting specially formatted PKCS#7 structures that trigger buffer overflows during decoding operations, particularly when the library processes email messages, code signing certificates, or secure communications protocols. The impact extends beyond immediate system crashes to potential privilege escalation scenarios where memory corruption could be leveraged for more sophisticated attacks.
The vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and represents a failure in input validation that violates fundamental security principles of bounds checking. From an ATT&CK framework perspective, this weakness maps to T1059.007 for command and script injection techniques, as well as T1499.004 for network denial of service attacks through memory corruption. The fix implemented in wolfSSL 5.9.1 demonstrates proper defensive programming practices by ensuring that all output buffer operations validate against caller-specified size parameters before writing data.
Organizations using affected wolfSSL versions should prioritize immediate patching to prevent exploitation, as the vulnerability creates a direct path for remote code execution in applications that process untrusted PKCS#7 content. System administrators should also implement monitoring for unusual memory access patterns and consider network segmentation to limit exposure of systems handling cryptographic operations. The mitigation strategy should include comprehensive testing of patched versions to ensure no regressions in functionality while maintaining the security improvements through proper bounds checking implementations.