CVE-2005-4900 in SHA-1
Summary
by MITRE
SHA-1 is not collision resistant, which makes it easier for context-dependent attackers to conduct spoofing attacks, as demonstrated by attacks on the use of SHA-1 in TLS 1.2. NOTE: this CVE exists to provide a common identifier for referencing this SHA-1 issue; the existence of an identifier is not, by itself, a technology recommendation.
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Analysis
by VulDB Data Team • 05/26/2026
The vulnerability described in CVE-2005-4900 addresses a fundamental weakness in the SHA-1 cryptographic hash function that has profound implications for digital security systems. This issue stems from the inherent mathematical properties of SHA-1 that make it susceptible to collision attacks, where two different inputs can produce identical hash outputs. The vulnerability is particularly concerning because it undermines the core security assumptions that cryptographic systems rely upon for integrity and authentication purposes.
The technical flaw in SHA-1 manifests through its vulnerability to collision resistance attacks, which were first demonstrated in 2005 when researchers showed that finding two distinct messages that produce the same SHA-1 hash was computationally feasible. This weakness directly impacts the security of TLS 1.2 implementations where SHA-1 is used for certificate signatures and message authentication. The context-dependent nature of these attacks means that attackers can exploit this vulnerability when they have control over the input data or can manipulate the cryptographic handshake process. The attack vectors typically involve creating fraudulent certificates or tampering with signed messages that rely on SHA-1 for integrity verification.
The operational impact of this vulnerability extends far beyond theoretical concerns, as it enables sophisticated spoofing attacks that can compromise the authenticity of communications and digital signatures. When SHA-1 is used in TLS 1.2, attackers can potentially generate fake certificates that appear valid to systems using SHA-1 for signature verification, leading to man-in-the-middle attacks and unauthorized access to secure communications. The vulnerability affects systems that depend on SHA-1 for certificate validation, digital signatures, and other security protocols where hash functions are used to ensure data integrity. This weakness has been exploited in real-world scenarios, including certificate authority compromises and security breaches where attackers leveraged SHA-1 collisions to impersonate legitimate entities.
Security practitioners should recognize that this vulnerability aligns with CWE-327, which specifically addresses the use of weak cryptographic algorithms, and relates to ATT&CK technique T1552.004 for credential access through the compromise of digital signatures and certificates. The recommended mitigations include immediate migration to stronger hash functions such as SHA-256 or SHA-3, discontinuing the use of SHA-1 in all security-critical applications, and implementing proper certificate validation procedures that do not rely on SHA-1. Organizations must also update their cryptographic libraries, review certificate chains, and ensure that all systems properly validate certificate signatures using robust hash algorithms to prevent exploitation of this fundamental weakness in cryptographic security.