CVE-2026-55964 Chain intermediate CA:TRUE without keyCertSign accepted as a signing CA (temporary CA exemption)
Attackers can bypass certificate validation checks in wolfSSL's OpenSSL compatibility mode by using intermediate CAs lacking keyCertSign, potentially enabling man-in-the-middle attacks.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-55964?
CVE-2026-55964 is a medium-severity vulnerability in Wolfssl Wolfssl, published on 25 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Chain intermediate CA:TRUE without keyCertSign accepted as a signing CA. Intermediate CA certificates are required to have the keyCertSign key usage when a Key Usage extension is present, but chain-supplied temporary CAs (WOLFSSL_TEMP_CA) added while building a certificate path were previously exempted from this check, so an intermediate asserting CA:TRUE but lacking keyCertSign was accepted as a signing CA. The check now applies to chain-supplied temporary CAs as well; only operator-loaded root certificates (WOLFSSL_USER_CA) and self-signed roots remain exempt. Per RFC 5280 an absent Key Usage extension implies all usages, so the requirement is enforced only when the extension is actually present (extKeyUsageSet). Affects the OpenSSL-compatibility certificate-path-building path (X509_verify_cert / X509_STORE, OPENSSL_EXTRA/OPENSSL_ALL), where untrusted chain intermediates are added as temporary CAs; native (non-OpenSSL-compat) certificate verification does not create temporary CAs and is unaffected. Within those builds, the check applies unless ALLOW_INVALID_CERTSIGN is defined.
Weakness: CWE-295
Which versions are affected by CVE-2026-55964?
It affects 1 product.
Products include Wolfssl Wolfssl.
How do I fix CVE-2026-55964?
Apply the vendor's patch.
Is CVE-2026-55964 being exploited?
There is no known exploitation of CVE-2026-55964 in the wild and no public exploit code.
Other vulnerabilities in Wolfssl Wolfssl
Sources
Also known as DEBIAN-CVE-2026-55964, GHSA-68g3-7fhp-7rg3, JLSEC-2026-738, UBUNTU-CVE-2026-55964.