The GNUtls woes continue, with another critical flaw discovered and patched after researchers worked out malicious servers could hijack users of the cryptographic library.

Red Hat engineer Nikos Mavrogiannopoulos, who issued a patch for the flaw (CVE-2014-3466) Saturday, shortly after it was reported 28 May by Codenomicon researcher Joonas Kuorilehto.

Users of other affected software will have to sit tight until their developers incorporate the fix. Until then, they'll remain open to malware attacks.

The vulnerability put GnuTLS back in the spotlight three months after Mavrogiannopoulos discovered the dangerous goto cleanup bug affecting the platform that allowed hackers to self-sign certificates which would be gobbled up by targeted sites.

That flaw affected more than 350 Linux software packages on distributions including Ubuntu, Debian and Red Hat which depended on GnuTLS libraries for secure sockets layer and transport layer security.

The new bug was described on the Red Hat bugtracker as a flaw in the way GnuTLS parsed session ids from Server Hello packets of the TLS/SSL handshake.

"A malicious server could use this flaw to send an excessively long session id value and trigger a buffer overflow in a connecting TLS/SSL client using GnuTLS, causing it to crash or, possibly, execute arbitrary code," the description read.

"The flaw is in read_server_hello() / _gnutls_read_server_hello(), where session_id_len is checked to not exceed incoming packet size, but not checked to ensure it does not exceed maximum session id length.

A deeper analysis including proof of concept was published on the Radare.Today blog.

Users should update the latest GnuTLS versions (3.1.25, 3.2.15 or 3.3.4). ®