NGINX

OpenSSL Patches HollowByte Vulnerability That Enables Denial-of-Service Attacks on TLS Connections with Just 11 Bytes

OpenSSL has released fixes for a vulnerability dubbed HollowByte that allows denial-of-service attacks against servers using unpatched versions of the library. The flaw can be triggered by a malicious TLS request as small as 11 bytes and was addressed without a CVE or formal security advisory because it was classified as a hardening improvement. Researchers from Okta warn that the operational impact can be significant on internet-facing servers, as the issue occurs during the initial TLS handshake when vulnerable OpenSSL versions reserve memory based on the client-declared size before verifying actual data delivery. Attackers can open connections, claim they will send a large message, and then deliver only a tiny portion, leaving the server waiting indefinitely with reserved memory. In tests with NGINX, low-memory servers could be completely taken down while more powerful machines suffered substantial capacity loss without triggering abnormal traffic volumes. The patches are included in OpenSSL versions 4.0.1, 3.6.3, 3.5.7, 3.4.6, and 3.0.21, and administrators are advised to update packages, restart affected services, and monitor for unusual memory growth.