Vulnerability-Lookup

CVE-2026-54736 (GCVE-0-2026-54736)

Vulnerability from cvelistv5 – Published: 2026-07-10 21:02 – Updated: 2026-07-13 18:01

Title

Phalcon: Non-constant-time HMAC verification in `Encryption\Crypt::decrypt` (timing side-channel)

Summary

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.

Severity

8.2 (High)


                        
                          CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-07-13 18:01 UTC

CWE

CWE-208 - Observable Timing Discrepancy
CWE-347 - Improper Verification of Cryptographic Signature

Assigner

GitHub_M mitre root

References

5 references

URL	Tags
https://github.com/phalcon/cphalcon/security/advi…	x_refsource_CONFIRM
https://github.com/phalcon/cphalcon/issues/17090	x_refsource_MISC
https://github.com/phalcon/cphalcon/pull/17091	x_refsource_MISC
https://github.com/phalcon/cphalcon/commit/ad53ab…	x_refsource_MISC
https://github.com/phalcon/cphalcon/releases/tag/…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
phalcon	cphalcon	Affected: < 5.14.1	guessed

Show details on NVD website

JSON

To clipboard

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                "id": "CVE-2026-54736",
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FKIE_CVE-2026-54736

Vulnerability from fkie_nvd - Published: 2026-07-10 22:16 - Updated: 2026-07-13 19:21

Severity

8.2 (High) - CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/phalcon/cphalcon/commit/ad53ab1b2e7ec59b3af92b0b37b8aaa099011137
	security-advisories@github.com	https://github.com/phalcon/cphalcon/issues/17090
	security-advisories@github.com	https://github.com/phalcon/cphalcon/pull/17091
	security-advisories@github.com	https://github.com/phalcon/cphalcon/releases/tag/v5.14.1
	security-advisories@github.com	https://github.com/phalcon/cphalcon/security/advisories/GHSA-8jqh-95g6-7jpj

Impacted products

	Vendor	Product	Version

JSON

To clipboard

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  "affected": [
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      "affectedData": [
        {
          "product": "cphalcon",
          "vendor": "phalcon",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 5.14.1"
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    }
  ],
  "id": "CVE-2026-54736",
  "lastModified": "2026-07-13T19:21:55.683",
  "metrics": {
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          "availabilityRequirement": "NOT_DEFINED",
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          "confidentialityRequirement": "NOT_DEFINED",
          "exploitMaturity": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
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          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
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GHSA-8JQH-95G6-7JPJ

Vulnerability from github – Published: 2026-08-28 16:01 – Updated: 2026-08-28 16:01

Summary

Phalcon: Non-constant-time HMAC verification in `Encryption\Crypt::decrypt` (timing side-channel)

Details

Summary

Phalcon\Encryption\Crypt provides authenticated encryption: when useSigning is enabled (the default), encrypt() appends an HMAC tag and decrypt() verifies it before returning the plaintext. The verification compares the attacker-supplied tag against the freshly computed HMAC using PHP/Zephir identity comparison (!==), which the Zephir compiler lowers to !ZEPHIR_IS_IDENTICAL(...) — a byte-wise memcmp that returns early on the first differing byte. The comparison time therefore depends on how many leading bytes of the supplied tag are correct, a classic MAC-verification timing side-channel. Every other secret/MAC comparison in the framework uses the constant-time hash_equals() (zephir_hash_equals) — the CSRF token check (Security::checkToken) and the JWT signature check (Signer\Hmac::verify); Crypt::decrypt is the lone deviation.

Details

Vulnerable code

phalcon/Encryption/Crypt.zep:246 (Zephir source):

if true === this->useSigning {
    // Checks on the decrypted message digest using the HMAC method.
    if digest !== hash_hmac(hashAlgorithm, padded, decryptKey, true) {
        throw new Mismatch("Hash does not match.");
    }
}

Generated C --> ext/phalcon/encryption/crypt.zep.c:364-367:

ZEPHIR_CALL_FUNCTION(&_8$$7, "hash_hmac", NULL, 245, &hashAlgorithm, &padded, &decryptKey, &__$true);
...
if (!ZEPHIR_IS_IDENTICAL(&digest, &_8$$7)) {                 // <-- non-constant-time
    ZEPHIR_THROW_EXCEPTION_DEBUG_STR(..., "Hash does not match.", "phalcon/Encryption/Crypt.zep", 247);

ZEPHIR_IS_IDENTICAL --> zephir_is_identical() (ext/kernel/operators.c:472) --> Zend is_identical_function --> for equal-length strings a memcmp that exits on the first mismatching byte (data-dependent timing).

Impact

The HMAC is the integrity/authentication tag of Phalcon's authenticated-encryption scheme. A successful timing attack (Keyczar/CVE-2009-0654-style: fix the IV+ciphertext so the target tag is constant, then recover it byte-by-byte from response timing) yields a tag the attacker can attach to a chosen IV+ciphertext so that decrypt() accepts it as authentic, defeating the integrity guarantee. Combined with CFB malleability (flipping a ciphertext byte flips the corresponding plaintext byte), an attacker who recovers the forging capability can tamper with the decrypted contents the application trusts (e.g. encrypted cookies carrying authorization/identity state). There is no confidentiality break by itself.

Suggested fix

Replace the identity comparison with the constant-time helper already used elsewhere in the framework. In phalcon/Encryption/Crypt.zep:246:

// before
if digest !== hash_hmac(hashAlgorithm, padded, decryptKey, true) {
    throw new Mismatch("Hash does not match.");
}
// after
if true !== hash_equals(hash_hmac(hashAlgorithm, padded, decryptKey, true), digest) {
    throw new Mismatch("Hash does not match.");
}

hash_equals() returns false for unequal-length inputs, so it also covers the truncated-tag case. Optional further hardening: verify the MAC before unpadding (functionally moot here because cryptUnpadText never throws) and consider migrating the default toward an AEAD mode such as aes-256-gcm.

Addressed Issue:

https://github.com/phalcon/cphalcon/issues/17090

Patched Stream:

https://github.com/phalcon/cphalcon/issues/17090

Severity

8.2 (High)


                  
                    CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 5.14.0"
      },
      "package": {
        "ecosystem": "Packagist",
        "name": "phalcon/cphalcon"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "5.14.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-54736"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-208",
      "CWE-347"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-08-28T16:01:05Z",
    "nvd_published_at": "2026-07-10T22:16:42Z",
    "severity": "HIGH"
  },
  "details": "## Summary\n\n`Phalcon\\Encryption\\Crypt` provides authenticated encryption: when `useSigning` is enabled (the default), `encrypt()` appends an HMAC tag and `decrypt()` verifies it before returning the plaintext. The verification compares the attacker-supplied tag against the freshly computed HMAC using PHP/Zephir identity comparison (`!==`), which the Zephir compiler lowers to `!ZEPHIR_IS_IDENTICAL(...)` \u2014 a byte-wise `memcmp` that returns early on the first differing byte. The comparison time therefore depends on how many leading bytes of the supplied tag are correct, a classic MAC-verification timing side-channel. Every other secret/MAC comparison in the framework uses the constant-time `hash_equals()` (`zephir_hash_equals`) \u2014 the CSRF token check (`Security::checkToken`) and the JWT signature check (`Signer\\Hmac::verify`); `Crypt::decrypt` is the lone deviation.\n\n## Details\n\n### Vulnerable code\n\n`phalcon/Encryption/Crypt.zep:246` (Zephir source):\n\n```zephir\nif true === this-\u003euseSigning {\n    // Checks on the decrypted message digest using the HMAC method.\n    if digest !== hash_hmac(hashAlgorithm, padded, decryptKey, true) {\n        throw new Mismatch(\"Hash does not match.\");\n    }\n}\n```\n\nGenerated C --\u003e `ext/phalcon/encryption/crypt.zep.c:364-367`:\n\n```c\nZEPHIR_CALL_FUNCTION(\u0026_8$$7, \"hash_hmac\", NULL, 245, \u0026hashAlgorithm, \u0026padded, \u0026decryptKey, \u0026__$true);\n...\nif (!ZEPHIR_IS_IDENTICAL(\u0026digest, \u0026_8$$7)) {                 // \u003c-- non-constant-time\n    ZEPHIR_THROW_EXCEPTION_DEBUG_STR(..., \"Hash does not match.\", \"phalcon/Encryption/Crypt.zep\", 247);\n```\n\n`ZEPHIR_IS_IDENTICAL` --\u003e `zephir_is_identical()` (`ext/kernel/operators.c:472`) --\u003e Zend `is_identical_function` --\u003e for equal-length strings a `memcmp` that exits on the first mismatching byte (data-dependent timing).\n\n\n\n### Impact\n\nThe HMAC is the integrity/authentication tag of Phalcon\u0027s authenticated-encryption scheme. A successful timing attack (Keyczar/CVE-2009-0654-style: fix the IV+ciphertext so the target tag is constant, then recover it byte-by-byte from response timing) yields a tag the attacker can attach to a chosen IV+ciphertext so that `decrypt()` accepts it as authentic, defeating the integrity guarantee. Combined with CFB malleability (flipping a ciphertext byte flips the corresponding plaintext byte), an attacker who recovers the forging capability can tamper with the decrypted contents the application trusts (e.g. encrypted cookies carrying authorization/identity state). There is no confidentiality break by itself.\n\n## Suggested fix\n\nReplace the identity comparison with the constant-time helper already used elsewhere in the framework. In `phalcon/Encryption/Crypt.zep:246`:\n\n```zephir\n// before\nif digest !== hash_hmac(hashAlgorithm, padded, decryptKey, true) {\n    throw new Mismatch(\"Hash does not match.\");\n}\n// after\nif true !== hash_equals(hash_hmac(hashAlgorithm, padded, decryptKey, true), digest) {\n    throw new Mismatch(\"Hash does not match.\");\n}\n```\n\n`hash_equals()` returns false for unequal-length inputs, so it also covers the truncated-tag case. Optional further hardening: verify the MAC before unpadding (functionally moot here because `cryptUnpadText` never throws) and consider migrating the default toward an AEAD mode such as `aes-256-gcm`.\n\nAddressed Issue: \n\n- https://github.com/phalcon/cphalcon/issues/17090\n\nPatched Stream: \n\n- https://github.com/phalcon/cphalcon/issues/17090",
  "id": "GHSA-8jqh-95g6-7jpj",
  "modified": "2026-08-28T16:01:05Z",
  "published": "2026-08-28T16:01:05Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/phalcon/cphalcon/security/advisories/GHSA-8jqh-95g6-7jpj"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-54736"
    },
    {
      "type": "WEB",
      "url": "https://github.com/phalcon/cphalcon/issues/17090"
    },
    {
      "type": "WEB",
      "url": "https://github.com/phalcon/cphalcon/pull/17091"
    },
    {
      "type": "WEB",
      "url": "https://github.com/phalcon/cphalcon/commit/ad53ab1b2e7ec59b3af92b0b37b8aaa099011137"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/phalcon/cphalcon"
    },
    {
      "type": "WEB",
      "url": "https://github.com/phalcon/cphalcon/releases/tag/v5.14.1"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Phalcon: Non-constant-time HMAC verification in `Encryption\\Crypt::decrypt` (timing side-channel)"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

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Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

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Action not permitted

CVE-2026-54736 (GCVE-0-2026-54736)

FKIE_CVE-2026-54736

GHSA-8JQH-95G6-7JPJ

Summary

Details

Vulnerable code

Impact

Suggested fix

Tags

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Nomenclature

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