Timing Attack in Phalcon Framework

Executive Summary

This vulnerability exists in the Phalcon PHP framework prior to version 5.14.1, specifically in the Phalcon\Encryption\Crypt::decrypt function. The issue arises because the function compares the attacker-supplied HMAC tag against a freshly computed HMAC using PHP/Zephir identity comparison, which effectively performs a byte-wise comparison that returns early when it finds the first differing byte.

This early return creates a timing discrepancy that an attacker can observe. By exploiting this timing difference, an attacker can recover a valid HMAC tag one byte at a time. Once the attacker has a valid tag, they can attach it to a chosen initialization vector (IV) and ciphertext, causing the decrypt() function to accept tampered encrypted content as authentic.

This vulnerability allows attackers to bypass the integrity check of encrypted data, potentially leading to unauthorized data manipulation.

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Impact Analysis

This vulnerability can impact you by allowing an attacker to tamper with encrypted data without detection. Because the decrypt() function can be tricked into accepting manipulated ciphertext as authentic, an attacker could alter sensitive information or inject malicious data.

Such unauthorized data manipulation can lead to data integrity breaches, potentially compromising application behavior, user data, or security controls that rely on the authenticity of encrypted content.

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Mitigation Strategies

To mitigate this vulnerability, you should upgrade Phalcon to version 5.14.1 or later, where the issue has been fixed.

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