Mojic: Observable Timing Discrepancy in HMAC Verification

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

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

Source published

24 Apr 2026 19:11:54 UTC

Source modified

24 Apr 2026 19:59:59 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 3.1 · 4.7 CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N

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

Source published

Apr 24, 2026, 7:11:54 PM (timezone not stated)

Source modified

Apr 24, 2026, 7:59:59 PM (timezone not stated)

Observed here

28 Oct 2026 05:07:21 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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EUVD CVSS 3.1 · 4.7 CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N

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

Source published

24 Apr 2026 20:16:26 UTC

Source modified

26 Oct 2026 21:10:00 UTC

Observed here

27 Oct 2026 10:10:07 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 4.7 CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N

### Summary The `CipherEngine` in Mojic v2.1.3 uses a standard equality operator (`!==`) to verify the HMAC-SHA256 integrity seal during the decryption phase. This creates an Observable Timing Discrepancy (CWE-208), allowing a potential attacker to bypass the file integrity check via a timing attack. ### Details In `lib/CipherEngine.js`, the footer check validates the HMAC signature using a standard string comparison: `if (footerHex !== calcDigest) { ... }` Standard string comparisons in JavaScript short-circuit; they return `false` the moment a character mismatch occurs. Because the time taken to evaluate the comparison is proportional to the number of matching leading bytes, an attacker can measure the exact microseconds it takes for the engine to throw the `FILE_TAMPERED` error. By repeatedly altering the signature byte-by-byte and analyzing these minute timing differences, a malicious actor can theoretically forge a valid HMAC signature without possessing the decryption password. ### PoC The vulnerable implementation is located in `lib/CipherEngine.js`, within the `getDecryptStream()` flush method (approximately line 265): ```javascript // Vulnerable Code if (footerHex !== calcDigest) { this.emit('error', new Error("FILE_TAMPERED")); return; } ``` ### Recommended Remediation: Replace the standard equality operator with Node.js's built-in constant-time comparison utility, crypto.timingSafeEqual(). ```JavaScript // Remediated Code const footerBuffer = Buffer.from(footerHex, 'hex'); const calcBuffer = Buffer.from(calcDigest, 'hex'); if (footerBuffer.length !== calcBuffer.length || !crypto.timingSafeEqual(footerBuffer, calcBuffer)) { this.emit('error', new Error("FILE_TAMPERED")); return; } ``` ### Impact If successfully exploited, an attacker could tamper with the encrypted .mojic payload and forge a valid HMAC signature. This bypasses the integrity seal, tricking the decryption engine into processing maliciously injected emoji streams. Because the engine translates these emojis back into C keywords and raw data chunks, this could ultimately result in arbitrary Code Injection into the restored .c source code when an unsuspecting user decrypts the tampered file.

Source published

16 Apr 2026 21:10:17 UTC

Source modified

5 May 2026 16:26:32 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N

Publisher rating · MODERATE