CVE-2026-41244: Mojic CLI Auth Bypass Vulnerability

CVE-2026-41244 Overview

Mojic is a CLI tool designed to transform readable C code into an unrecognizable chaotic stream of emojis. Prior to version 2.1.4, the CipherEngine component uses a standard equality operator (!==) to verify the HMAC-SHA256 integrity seal during the decryption phase. This implementation creates an Observable Timing Discrepancy (CWE-208), allowing a potential attacker to bypass the file integrity check via a timing attack.

Critical Impact
Attackers can exploit timing differences in HMAC comparison to bypass file integrity verification, potentially allowing tampered or malicious files to be processed as legitimate.

Affected Products

Mojic CLI Tool versions prior to 2.1.4

Discovery Timeline

2026-04-24 - CVE CVE-2026-41244 published to NVD
2026-04-28 - Last updated in NVD database

Technical Details for CVE-2026-41244

Vulnerability Analysis

This vulnerability stems from an insecure implementation of HMAC-SHA256 verification in Mojic's CipherEngine component. The flaw lies in using a standard string comparison operator (!==) instead of a constant-time comparison function when validating the integrity seal during the decryption process.

When the CipherEngine verifies an HMAC signature, the standard comparison operator performs a byte-by-byte check that exits early upon finding the first mismatched byte. This early-exit behavior creates measurable timing differences—valid byte prefixes take slightly longer to compare than completely invalid ones. An attacker can exploit these microsecond-level timing variations to progressively reconstruct a valid HMAC signature, ultimately bypassing the integrity verification mechanism entirely.

The impact centers on integrity compromise. While this attack requires local access and user interaction, successful exploitation could allow an attacker to modify encrypted files and have them accepted as authentic, potentially leading to code manipulation or injection of malicious payloads.

Root Cause

The root cause is the use of a non-constant-time comparison operation for cryptographic verification. The CipherEngine's HMAC-SHA256 verification code employs the standard inequality operator (!==) which performs early termination upon finding a mismatch. For cryptographic operations, a constant-time comparison function should be used that always compares all bytes regardless of where mismatches occur, preventing timing side-channel information leakage.

Attack Vector

The attack vector requires local access to the system where Mojic is installed. An attacker must be able to interact with the decryption functionality and precisely measure the time taken for HMAC verification attempts. By submitting numerous decryption requests with carefully crafted HMAC values and analyzing response times, the attacker can statistically determine which bytes of the HMAC are correct, gradually building a valid signature byte-by-byte.

The timing attack methodology involves:

Submitting trial HMAC values with variations in specific byte positions
Measuring response times with high precision
Using statistical analysis to identify which byte values produce longer verification times
Iterating through each byte position to reconstruct the full valid HMAC

For technical details on this vulnerability, see the GitHub Security Advisory.

Detection Methods for CVE-2026-41244

Indicators of Compromise

Unusual patterns of repeated decryption requests against the same file
High-frequency API calls to the CipherEngine verification functions
Network traffic or system logs showing sequential HMAC verification attempts with minor variations
Abnormal processing times associated with decryption operations

Detection Strategies

Monitor for repetitive decryption operations targeting identical encrypted content
Implement rate limiting on HMAC verification attempts to frustrate timing analysis
Deploy application-level logging to capture verification failure patterns
Use anomaly detection to identify statistical probing behavior characteristic of timing attacks

Monitoring Recommendations

Enable verbose logging for Mojic CLI operations, particularly decryption activities
Track failed HMAC verification attempts and alert on unusual frequency or patterns
Monitor system timing and CPU usage during decryption operations for anomalies
Review application logs for signs of automated or scripted interaction with the decryption functionality

How to Mitigate CVE-2026-41244

Immediate Actions Required

Upgrade Mojic CLI to version 2.1.4 or later immediately
Review any files that were decrypted using vulnerable versions for integrity
Audit systems for signs of exploitation or unusual decryption activity patterns
Restrict access to the Mojic CLI tool to trusted users only

Patch Information

This vulnerability is fixed in Mojic version 2.1.4. The fix replaces the vulnerable standard equality comparison with a constant-time comparison function that takes the same amount of time regardless of where byte mismatches occur, eliminating the timing side-channel. Users should update immediately by obtaining the latest release from the official repository. Additional details are available in the GitHub Security Advisory.

Workarounds

If immediate upgrade is not possible, restrict access to the Mojic CLI tool to trusted users and environments
Implement network-level rate limiting on systems running the vulnerable tool
Consider disabling decryption functionality until the patch can be applied
Monitor for signs of exploitation while awaiting upgrade deployment