CVE-2015-0832 in Firefox
Summary
by MITRE
Mozilla Firefox before 36.0 does not properly recognize the equivalence of domain names with and without a trailing . (dot) character, which allows man-in-the-middle attackers to bypass the HPKP and HSTS protection mechanisms by constructing a URL with this character and leveraging access to an X.509 certificate for a domain with this character.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 03/10/2022
The vulnerability described in CVE-2015-0832 represents a critical flaw in Mozilla Firefox's certificate validation mechanism that undermines fundamental web security protocols. This issue specifically affects Firefox versions prior to 36.0 and stems from the browser's failure to properly handle domain name equivalence when comparing certificate subjects against requested hostnames. The technical flaw manifests when a certificate is issued for a domain name that includes a trailing dot character, which is a valid DNS format but often overlooked in security implementations. The vulnerability exploits the fact that certain web servers and applications may accept connections for domains with or without trailing dots, creating a potential attack vector for malicious actors seeking to bypass security protections.
The operational impact of this vulnerability is significant as it directly compromises two critical security mechanisms: HTTP Public Key Pinning (HPKP) and HTTP Strict Transport Security (HSTS). Both of these protocols rely on accurate domain name matching to ensure that clients only trust certificates issued for the intended domain. When Firefox fails to recognize that a domain name with and without a trailing dot are equivalent, attackers can craft malicious URLs that appear legitimate to the browser while actually connecting to a server controlled by the attacker. This bypass allows malicious actors to perform man-in-the-middle attacks without triggering security warnings, effectively neutralizing the protections that these security mechanisms are designed to provide.
The security implications extend beyond simple certificate validation failures and represent a fundamental weakness in how the browser processes domain name comparisons during SSL/TLS handshakes. This flaw demonstrates a critical gap in Firefox's certificate verification logic that aligns with CWE-295, which addresses improper certificate validation. Attackers can exploit this vulnerability by obtaining a certificate for a domain with a trailing dot and then constructing URLs that appear to target the standard domain format, thereby tricking the browser into accepting the certificate as valid for the intended target. The vulnerability also relates to ATT&CK technique T1552.001, which covers credentials from password storage components, as it allows attackers to bypass security mechanisms that would normally prevent such credential interception.
Mitigation strategies for this vulnerability include immediate upgrading to Firefox version 36.0 or later, where the issue has been resolved through enhanced domain name comparison logic. Organizations should also implement additional monitoring for suspicious certificate usage patterns and ensure that their security infrastructure properly validates certificate subject names against expected domain formats. The fix implemented by Mozilla addresses the core issue by ensuring that domain name comparisons properly account for trailing dot equivalence, thereby maintaining the integrity of HPKP and HSTS protections. Security teams should also consider implementing additional certificate monitoring solutions to detect and respond to potential exploitation attempts involving this specific vulnerability.