What’s Vulnerable › Vulnerabilities

CVE-2023-6936: Heap-buffer over-read with WOLFSSL_CALLBACKS

• Severity: critical (CVSS 9.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2024-02-20 · updated 2026-06-17
• Weakness: CWE-125

Description

In wolfSSL prior to 5.6.6, if callback functions are enabled (via the WOLFSSL_CALLBACKS flag), then a malicious TLS client or network attacker can trigger a buffer over-read on the heap of 5 bytes (WOLFSSL_CALLBACKS is only intended for debugging).

Affected products

• wolfSSL: before 5.6.6 — fixed in 5.6.6

How to fix

Upgrade to a fixed version: wolfSSL 5.6.6. Check the vendor advisory for mitigations.

References

• https://github.com/wolfSSL/wolfssl/pull/6949/
• https://www.wolfssl.com/docs/security-vulnerabilities/
• https://github.com/wolfSSL/wolfssl/pull/6949/
• https://www.wolfssl.com/docs/security-vulnerabilities/

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