Mozilla Network Security Services (NSS), as used in Mozilla Firefox is vulnerable to a heap-based buffer overflow, caused by improper bounds checking when using certain cryptographic primitives. By sending an overly long argument, a remote attacker could overflow a buffer and execute arbitrary code on the system or cause a denial of service.

Mozilla Network Security Services (NSS) before 3.23, as used in Mozilla Firefox before 47.0, allows remote attackers to cause a denial of service (memory corruption and application crash) or possibly have unspecified other impact via unknown vectors.

Heap-based buffer overflow in the ASN.1 decoder in Mozilla Network Security Services (NSS) before 3.19.2.1 and 3.20.x before 3.20.1, as used in Firefox before 42.0 and Firefox ESR 38.x before 38.4 and other products, allows remote attackers to cause a denial of service (application crash) or possibly execute arbitrary code via crafted OCTET STRING data.

Mozilla Firefox and Thunderbird could allow a remote attacker to execute arbitrary code on the system, caused by a use-after-free error in the PK11ImportCert() function when adding NSSCertificate structures. By persuading a victim to visit a specially-crafted Web site, a remote attacker could exploit this vulnerability using unknown attack vectors to execute arbitrary code on the vulnerable system or cause a denial of service.

A heap overflow flaw was found in a regular expression parser in the NSS library used to match common names in certificates. A malicious site could present a carefully crafted certificate in such a way as to trigger the heap overflow leading to a crash or possibly execute arbitrary code as the user running a browser such as firefox.

The overflow happens when the browser checks if the hostname of the site you are visiting matches the Common Name (CN) field of the presented certificate. This check (certTestHostName) only happens automatically if the certificate is one that is signed by a Certificate Authority you have previously trusted. If the attacker presents a malicious self-signed certificate, or one signed by an untrusted CA, the user is presented with a dialog box about the certificate before the vulnerable function is called. If the user chooses to accept the certificate then the vulnerable function is called and the heap overflow happens. So this issue does require slightly more user interaction to be exploited.

Co-incidentally, the handling of regular expressions for NSS versions 3.12.3 and above was changed to use a different and simpler regular expression routine which is not vulnerable to this issue. Therefore where a system has NSS 3.12.3 installed, it is not vulnerable to this issue by default. (Although it is possible to change Firefox back to use the old vulnerable library it is not something that is expected users to have done, and is not an obvious documented ability)

For Red Hat Enterprise Linux 5, Firefox uses the system provided NSS library. This library was updated to a versions greater than 3.12.3 by RHBA-2009:1161 on 20th July 2009. Therefore systems updated to RHBA-2009:1161 are protected by default from this issue.

For Red Hat Enterprise Linux 4, Firefox uses the system provided NSS library. This library is due to be updated to a version greater than 3.12.3 and this will probably happen within the week (so before the embargo lifts).

For Red Hat Enterprise Linux 3 we do not ship Firefox but instead SeaMonkey which provides the NSS library. SeaMonkey will need updating to correct this issue.