CVE-2015-2808 in HTTP Server
Summary
by MITRE
The RC4 algorithm, as used in the TLS protocol and SSL protocol, does not properly combine state data with key data during the initialization phase, which makes it easier for remote attackers to conduct plaintext-recovery attacks against the initial bytes of a stream by sniffing network traffic that occasionally relies on keys affected by the Invariance Weakness, and then using a brute-force approach involving LSB values, aka the "Bar Mitzvah" issue.
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Analysis
by VulDB Data Team • 05/28/2026
The vulnerability described in CVE-2015-2808 represents a critical weakness in the RC4 stream cipher implementation within TLS and SSL protocols, fundamentally undermining the security guarantees these cryptographic standards are designed to provide. This flaw specifically targets the initialization phase of RC4 where the algorithm fails to adequately mix the key material with the internal state data, creating predictable patterns that can be exploited by adversaries. The issue is particularly concerning because RC4 was widely deployed in web applications and secure communications, making it a prime target for attackers seeking to compromise encrypted data transmission. The vulnerability stems from what is known as the Invariance Weakness, where certain bytes of the RC4 keystream remain predictable even when the key changes, creating a pathway for cryptanalytic attacks that can recover plaintext information from encrypted communications.
The technical exploitation of this vulnerability follows a well-documented attack pattern that leverages the predictable nature of RC4's output during the initial bytes of the keystream generation process. Attackers can perform plaintext-recovery attacks by capturing network traffic that utilizes RC4 encryption and then applying brute-force techniques focusing on the least significant bits of the keystream values. This approach, dubbed the "Bar Mitzvah" attack, takes advantage of the mathematical properties of RC4's pseudo-random generation algorithm where the first few bytes of the output stream exhibit statistical biases that correlate with the input key. The attack becomes particularly effective when the same key is used for multiple connections or when network traffic patterns provide sufficient information about the plaintext content. According to CWE-327, this vulnerability directly relates to the use of weak cryptographic algorithms and improper implementation of cryptographic primitives, specifically targeting the fundamental security requirements of confidentiality and integrity in network communications.
The operational impact of CVE-2015-2808 extends far beyond individual security incidents, affecting the entire ecosystem of web applications and services that relied on RC4 encryption. Organizations implementing TLS and SSL protocols using RC4 were exposed to significant risks including data interception, man-in-the-middle attacks, and potential compromise of sensitive information transmitted over the network. The vulnerability's exploitation does not require extremely sophisticated tools or extensive computational resources, making it accessible to a wide range of threat actors from script kiddies to organized cybercriminal groups. Security professionals noted that the attack could be particularly devastating in environments where the same keys were reused across multiple sessions or where attackers could observe patterns in network traffic that provided additional context for their brute-force efforts. This weakness directly violates the principles outlined in the NIST SP 800-57 standard for cryptographic key management and the CIA triad requirements for maintaining confidentiality in secure communications.
Mitigation strategies for CVE-2015-2808 required immediate action across the cybersecurity community, with organizations needing to disable RC4 support in their cryptographic implementations as a primary defense measure. The recommended approach involved implementing protocol-level changes that enforced the use of stronger encryption algorithms such as AES-GCM or ChaCha20-Poly1305, which do not suffer from the same mathematical weaknesses as RC4. Security administrators were advised to conduct comprehensive audits of their cryptographic configurations and ensure that all systems properly implemented the TLS protocol version 1.2 or higher, which explicitly deprecates RC4 in favor of more secure alternatives. The mitigation process also required updates to web server configurations, client applications, and network infrastructure components that might still be using RC4 encryption. According to ATT&CK framework's T1046 technique for network service scanning, organizations needed to monitor for continued use of vulnerable RC4 implementations and ensure complete removal of the algorithm from all cryptographic libraries and protocols. The vulnerability highlighted the importance of continuous cryptographic assessment and the need for organizations to maintain current knowledge of cryptographic vulnerabilities, as outlined in the ISO/IEC 27001 information security management standards.