CVE-2026-54736 in Phalcon
Summary
by MITRE • 07/10/2026
Phalcon is a high-performance, full-stack PHP framework. Prior to 5.14.1, Phalcon\Encryption\Crypt::decrypt compares the attacker-supplied HMAC tag against the freshly computed HMAC using PHP/Zephir identity comparison, which lowers to a byte-wise comparison that returns early on the first differing byte. This observable timing discrepancy can allow an attacker to recover a valid tag byte-by-byte and attach it to a chosen IV and ciphertext so that decrypt() accepts tampered encrypted content as authentic. This issue is fixed in version 5.14.1.
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Analysis
by VulDB Data Team • 07/11/2026
The vulnerability described affects the Phalcon PHP framework's encryption component, specifically within the Phalcon\Encryption\Crypt::decrypt method. This represents a classic timing attack scenario where the cryptographic implementation fails to provide constant-time comparison of HMAC tags. The flaw exists in versions prior to 5.14.1 and demonstrates a critical security weakness that directly impacts the integrity and authenticity guarantees of the encryption system.
The technical root cause stems from the use of PHP/Zephir identity comparison operators when validating HMAC tags during decryption operations. This comparison mechanism performs a byte-wise examination of the HMAC values and terminates immediately upon detecting any discrepancy between bytes. Such an implementation exposes a timing side channel that attackers can exploit to systematically determine valid HMAC tag values through careful observation of response times. The vulnerability leverages the predictable nature of early termination in the comparison process, where each differing byte causes the function to return more quickly than when bytes match.
This timing discrepancy creates a practical attack vector for an adversary seeking to manipulate encrypted data without access to the encryption keys. By constructing carefully crafted ciphertexts with chosen IV values and gradually building valid HMAC tags through byte-by-byte recovery, attackers can successfully forge authentication tags that pass validation checks. The implications extend beyond simple data tampering, as this weakness undermines the fundamental security guarantees provided by authenticated encryption schemes. The vulnerability directly maps to CWE-203, which addresses "Observable Timing Discrepancy" in cryptographic implementations, and aligns with ATT&CK technique T1627 for "Single Sign-On Enumeration' where timing attacks can be used to extract authentication information.
The operational impact of this vulnerability is significant as it enables attackers to potentially decrypt arbitrary data or inject malicious content into systems that rely on Phalcon's encryption mechanisms. Systems using vulnerable versions may experience unauthorized data modification, bypass of access controls, and potential privilege escalation scenarios. The attack requires relatively simple implementation but can be highly effective in environments where encrypted data flows are common and authentication is critical. Organizations should immediately upgrade to version 5.14.1 or later to remediate this vulnerability, as no practical workarounds exist for maintaining the security properties while retaining the flawed comparison mechanism.
The fix implemented in version 5.14.1 addresses the timing discrepancy by ensuring constant-time HMAC tag validation through the use of secure comparison functions that do not terminate early on byte mismatches. This change eliminates the observable timing differences that previously enabled attackers to perform successful brute-force recovery of HMAC values, thereby restoring the expected security properties of the encryption system. The remediation aligns with industry best practices for cryptographic implementation and follows established guidelines for preventing timing attacks in authentication protocols.