CVE-2010-0731: Buffer Overflow

During the testing of GnuTLS updates, a flaw was discovered affecting Red Hat Enterprise Linux 4 GnuTLS packages on s390x platform, causing gnutls-cli to crash while printing server certificate info.

This crash was caused by a flaw in gnutlsx509crtgetserial(), which calls asn1readvalue() to extract serial number from the x509 certificate.

(lib/x509/x509.c) 526 int gnutlsx509crtgetserial(gnutlsx509crt cert, void result, 527 sizet resultsize) 528 { ... 536 if ((ret = asn1readvalue(cert->cert, "tbsCertificate.serialNumber", result, resultsize)) < 0) {

asn1readvalue() expects pointer to int (32 bit) as its third argument, but gnutlsx509crtgetserial() passed pointer to sizet (64 bit on 64 bit platforms) instead. On 64bit big endian platforms asn1readvalue() got incorrect length value.

(lib/minitasn1/element.c) 598 asn1retCode 599 asn1readvalue(nodeasn root,const char name,void ivalue, int len)

On little endian 64 bit platforms, high 32 bits of the resultsize sizet value were lost, but they only contained zeros. On big endian 64 bit platforms, low 32 bits were lost / ignored, causing asn1readvalue() to see length value as 0. This caused asn1readvalue() to return an error, but the length of the value that should have been extracted was saved to len.

gnutlsx509crtgetserial() did not correctly check return value of asn1readvalue(), failing to detect an error. After returning, caller could see a high value stored in resultsize (when interpreted as 64 bit value again).

printx509info() (used by gnutls-cli or gnutls-serv) and printcertificateinfo() (used by certtool) relied on the returned size value. Unexpected value caused a stack buffer overflow in those functions.

This bug could also cause gnutlsx509crtcheckrevocation() to incorrectly check supplied X509 certificate against the list of revoked certificates, resulting in a bypass or the CRL check.

This issue was fixed upstream via following commit: http://git.savannah.gnu.org/cgit/gnutls.git/commit/?id=112d537d

This fix was first included in upstream version 1.2.1. Therefore, GnuTLS packages in Red Hat Enterprise Linux 5, Fedora, and current upstream GnuTLS versions are not affected by this flaw.