Security vulnerability: wolfSSL library accepts manipulated certificates

Due to a security vulnerability in the TLS library wolfSSL, attackers can lure victims to servers they control under the guise of a trustworthy connection. To prevent this, admins should install the patched version. In a recent release, the developers have closed further vulnerabilities.

As the changelog of the current version 5.9.1 shows , the developers have addressed a total of 21 security issues. The most dangerous is a “ critical ” vulnerability (CVE-2026-5194) affecting certificate handling. Because errors occur when dealing with signatures issued via ECDSA/ECC or DSA, attackers can manipulate certificates, which are then accepted as valid. This allows attackers to lure victims to servers they control within a seemingly trustworthy connection.

Nine further software vulnerabilities are classified as “ high ” threat level. If attackers exploit these vulnerabilities successfully, they can trigger memory errors (e.g., CVE-2026-5264). This usually leads to crashes, but in such contexts, malware often also gets onto systems.

If attackers exploit the remaining vulnerabilities, memory errors (e.g., CVE-2026-5392 “ medium”) can also occur, or attackers can view actually encrypted content in plain text (CVE-2026-5504 “ medium ”).

So far, there are no indications of attacks. However, admins should not delay installing the version equipped against the described possible attacks. Otherwise, the security of connections is not guaranteed.

This article was originally published in German . It was translated with technical assistance and editorially reviewed before publication.