{"id":"CVE-2025-62494","aliases":["DEBIAN-CVE-2025-62494","EUVD-2025-34780","GHSA-7gcv-76g2-94qm","UBUNTU-CVE-2025-62494"],"status":"published","title":"Type confusion in string addition in QuickJS","description":"A type confusion vulnerability exists in the handling of the string addition (+) operation within the QuickJS engine.\n\n  *  The code first checks if the left-hand operand is a string.\n\n\n  *  It then attempts to convert the right-hand operand to a primitive value using JS_ToPrimitiveFree. This conversion can trigger a callback (e.g., toString or valueOf).\n\n\n  *  During this callback, an attacker can modify the type of the left-hand operand in memory, changing it from a string to a different type (e.g., an object or an array).\n\n\n  *  The code then proceeds to call JS_ConcatStringInPlace, which still treats the modified left-hand value as a string.\n\n\nThis mismatch between the assumed type (string) and the actual type allows an attacker to control the data structure being processed by the concatenation logic, resulting in a type confusion condition. This can lead to out-of-bounds memory access, potentially resulting in memory corruption and arbitrary code execution in the context of the QuickJS runtime.","severity":{"version":"4.0","score":7.1,"vector":"CVSS:4.0/AV:A/AC:H/AT:P/PR:L/UI:P/VC:H/VI:H/VA:L/SC:H/SI:H/SA:L","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-12","score":0.00526,"percentile":0.45067,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":false},"cwes":["CWE-704"],"published":"2025-10-16T15:51:50Z","modified":"2026-10-23T17:47:26Z","affected":[{"source":"osv","ecosystem":"Debian:13","package":"quickjs","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2025.04.26-1"]},{"source":"osv","ecosystem":"Debian:14","package":"quickjs","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2025.04.26-1"]},{"source":"osv","ecosystem":"Ubuntu:Pro:24.04:LTS","package":"quickjs","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2021.03.27-1","2021.03.27-1ubuntu0.1~esm1"]},{"source":"osv","ecosystem":"Ubuntu:25.10","package":"quickjs","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2024.01.13-5","2025.04.26-1"]},{"source":"osv","ecosystem":"Ubuntu:26.10","package":"quickjs","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2025.04.26-1build1"]},{"source":"osv","ecosystem":"Ubuntu:26.04:LTS","package":"quickjs","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2025.04.26-1","2025.04.26-1build1"]}],"products":[{"vendor":"quickjs","product":"quickjs"},{"vendor":"quickjs-ng","product":"quickjs"},{"vendor":"quickjs_project","product":"quickjs"}],"references":[{"url":"https://bellard.org/quickjs/Changelog","tags":["Release Notes","advisory","report"]},{"url":"https://issuetracker.google.com/434193023","tags":["Exploit","Issue Tracking","report"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2025-62494"},{"url":"https://github.com/advisories/GHSA-7gcv-76g2-94qm"},{"url":"https://security-tracker.debian.org/tracker/CVE-2025-62494","tags":["advisory"]},{"url":"https://ubuntu.com/security/CVE-2025-62494","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2025-62494","tags":["report"]}],"sources":{"cve":[{"id":"CVE-2025-62494","title":"Type confusion in string addition in QuickJS","description":"A type confusion vulnerability exists in the handling of the string addition (+) operation within the QuickJS engine.\n\n  *  The code first checks if the left-hand operand is a string.\n\n\n  *  It then attempts to convert the right-hand operand to a primitive value using JS_ToPrimitiveFree. This conversion can trigger a callback (e.g., toString or valueOf).\n\n\n  *  During this callback, an attacker can modify the type of the left-hand operand in memory, changing it from a string to a different type (e.g., an object or an array).\n\n\n  *  The code then proceeds to call JS_ConcatStringInPlace, which still treats the modified left-hand value as a string.\n\n\nThis mismatch between the assumed type (string) and the actual type allows an attacker to control the data structure being processed by the concatenation logic, resulting in a type confusion condition. This can lead to out-of-bounds memory access, potentially resulting in memory corruption and arbitrary code execution in the context of the QuickJS runtime.","status":"published","published":"2025-10-16T15:51:50.977Z","modified":"2025-10-16T17:46:39.174Z","cvss":[{"version":"4.0","score":7.1,"vector":"CVSS:4.0/AV:A/AC:H/AT:P/PR:L/UI:P/VC:H/VI:H/VA:L/SC:H/SI:H/SA:L","level":"high","assessor":"cna"}],"cwes":["CWE-704"],"updated_at":"2026-11-02T14:32:54.87586Z"}],"euvd":[{"id":"EUVD-2025-34780","description":"A type confusion vulnerability exists in the handling of the string addition (+) operation within the QuickJS engine.\n\n  *  The code first checks if the left-hand operand is a string.\n\n\n  *  It then attempts to convert the right-hand operand to a primitive value using JS_ToPrimitiveFree. This conversion can trigger a callback (e.g., toString or valueOf).\n\n\n  *  During this callback, an attacker can modify the type of the left-hand operand in memory, changing it from a string to a different type (e.g., an object or an array).\n\n\n  *  The code then proceeds to call JS_ConcatStringInPlace, which still treats the modified left-hand value as a string.\n\n\nThis mismatch between the assumed type (string) and the actual type allows an attacker to control the data structure being processed by the concatenation logic, resulting in a type confusion condition. This can lead to out-of-bounds memory access, potentially resulting in memory corruption and arbitrary code execution in the context of the QuickJS runtime.","status":"published","published":"2025-10-16T15:51:50Z","modified":"2025-10-16T17:46:39Z","cvss":[{"version":"4.0","score":7.1,"vector":"CVSS:4.0/AV:A/AC:H/AT:P/PR:L/UI:P/VC:H/VI:H/VA:L/SC:H/SI:H/SA:L","level":"high"}],"updated_at":"2026-11-02T20:31:31.065489Z"}],"ghsa":[{"id":"GHSA-7gcv-76g2-94qm","title":"A type confusion vulnerability exists in the handling of the string addition (+) operation within...","description":"A type confusion vulnerability exists in the handling of the string addition (+) operation within the QuickJS engine.\n\n  *  The code first checks if the left-hand operand is a string.\n\n\n  *  It then attempts to convert the right-hand operand to a primitive value using JS_ToPrimitiveFree. This conversion can trigger a callback (e.g., toString or valueOf).\n\n\n  *  During this callback, an attacker can modify the type of the left-hand operand in memory, changing it from a string to a different type (e.g., an object or an array).\n\n\n  *  The code then proceeds to call JS_ConcatStringInPlace, which still treats the modified left-hand value as a string.\n\n\nThis mismatch between the assumed type (string) and the actual type allows an attacker to control the data structure being processed by the concatenation logic, resulting in a type confusion condition. This can lead to out-of-bounds memory access, potentially resulting in memory corruption and arbitrary code execution in the context of the QuickJS runtime.","status":"published","published":"2025-10-16T18:30:24Z","modified":"2025-10-29T21:30:33Z","cvss":[{"version":"4.0","score":7.1,"vector":"CVSS:4.0/AV:A/AC:H/AT:P/PR:L/UI:P/VC:H/VI:H/VA:L/SC:H/SI:H/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:X/U:X","level":"high"},{"version":"3.1","score":8.8,"vector":"CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"high"}],"cwes":["CWE-704"],"updated_at":"2026-11-02T15:04:15.305123Z"}],"nvd":[{"id":"CVE-2025-62494","description":"A type confusion vulnerability exists in the handling of the string addition (+) operation within the QuickJS engine.\n\n  *  The code first checks if the left-hand operand is a string.\n\n\n  *  It then attempts to convert the right-hand operand to a primitive value using JS_ToPrimitiveFree. This conversion can trigger a callback (e.g., toString or valueOf).\n\n\n  *  During this callback, an attacker can modify the type of the left-hand operand in memory, changing it from a string to a different type (e.g., an object or an array).\n\n\n  *  The code then proceeds to call JS_ConcatStringInPlace, which still treats the modified left-hand value as a string.\n\n\nThis mismatch between the assumed type (string) and the actual type allows an attacker to control the data structure being processed by the concatenation logic, resulting in a type confusion condition. This can lead to out-of-bounds memory access, potentially resulting in memory corruption and arbitrary code execution in the context of the QuickJS runtime.","status":"published","published":"2025-10-16T16:15:39.943Z","modified":"2026-10-19T16:10:00.26Z","cvss":[{"version":"4.0","score":7.1,"vector":"CVSS:4.0/AV:A/AC:H/AT:P/PR:L/UI:P/VC:H/VI:H/VA:L/SC:H/SI:H/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:X/U:X","level":"high","assessor":"secondary"},{"version":"3.1","score":8.8,"vector":"CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"high","assessor":"primary"}],"cwes":["CWE-704"],"updated_at":"2026-11-02T14:11:39.069866Z"}],"osv":[{"id":"CVE-2025-62494","description":"A type confusion vulnerability exists in the handling of the string addition (+) operation within the QuickJS engine.\n\n  *  The code first checks if the left-hand operand is a string.\n\n\n  *  It then attempts to convert the right-hand operand to a primitive value using JS_ToPrimitiveFree. This conversion can trigger a callback (e.g., toString or valueOf).\n\n\n  *  During this callback, an attacker can modify the type of the left-hand operand in memory, changing it from a string to a different type (e.g., an object or an array).\n\n\n  *  The code then proceeds to call JS_ConcatStringInPlace, which still treats the modified left-hand value as a string.\n\n\nThis mismatch between the assumed type (string) and the actual type allows an attacker to control the data structure being processed by the concatenation logic, resulting in a type confusion condition. This can lead to out-of-bounds memory access, potentially resulting in memory corruption and arbitrary code execution in the context of the QuickJS runtime.","status":"published","published":"2025-10-16T16:15:39.943Z","modified":"2026-04-10T05:33:07.437092Z","cvss":[{"version":"3.1","score":8.8,"vector":"CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"high"}],"updated_at":"2026-11-02T15:44:51.851511Z"},{"id":"DEBIAN-CVE-2025-62494","description":"A type confusion vulnerability exists in the handling of the string addition (+) operation within the QuickJS engine.    *  The code first checks if the left-hand operand is a string.     *  It then attempts to convert the right-hand operand to a primitive value using JS_ToPrimitiveFree. This conversion can trigger a callback (e.g., toString or valueOf).     *  During this callback, an attacker can modify the type of the left-hand operand in memory, changing it from a string to a different type (e.g., an object or an array).     *  The code then proceeds to call JS_ConcatStringInPlace, which still treats the modified left-hand value as a string.   This mismatch between the assumed type (string) and the actual type allows an attacker to control the data structure being processed by the concatenation logic, resulting in a type confusion condition. This can lead to out-of-bounds memory access, potentially resulting in memory corruption and arbitrary code execution in the context of the QuickJS runtime.","status":"published","published":"2025-10-16T16:15:39.943Z","modified":"2026-10-23T17:47:26.661149007Z","cvss":[{"version":"3.1","score":8.8,"vector":"CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"high"}],"updated_at":"2026-11-02T15:45:47.697959Z"},{"id":"UBUNTU-CVE-2025-62494","description":"A type confusion vulnerability exists in the handling of the string addition (+) operation within the QuickJS engine.   *  The code first checks if the left-hand operand is a string.   *  It then attempts to convert the right-hand operand to a primitive value using JS_ToPrimitiveFree. This conversion can trigger a callback (e.g., toString or valueOf).   *  During this callback, an attacker can modify the type of the left-hand operand in memory, changing it from a string to a different type (e.g., an object or an array).   *  The code then proceeds to call JS_ConcatStringInPlace, which still treats the modified left-hand value as a string. This mismatch between the assumed type (string) and the actual type allows an attacker to control the data structure being processed by the concatenation logic, resulting in a type confusion condition. This can lead to out-of-bounds memory access, potentially resulting in memory corruption and arbitrary code execution in the context of the QuickJS runtime.","status":"published","published":"2025-10-16T16:15:00Z","modified":"2026-10-17T12:57:27.878606465Z","cvss":[{"version":"4.0","score":7.1,"vector":"CVSS:4.0/AV:A/AC:H/AT:P/PR:L/UI:P/VC:H/VI:H/VA:L/SC:H/SI:H/SA:L","level":"high"},{"version":"3.1","score":8.8,"vector":"CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"high"}],"updated_at":"2026-11-02T16:55:50.817402Z"}]}}