{"schemaVersion":3,"id":"CVE-2026-103435","aliases":[],"status":"published","duplicateOf":null,"title":"Arbitrary File Write via Write-Time Symlink Following (TOCTOU) in Claude Code","description":"Claude Code validated that a target file path resided within the project working directory at permission-check time, but re-resolved the path at write time without repeating that validation. This time-of-check to time-of-use (TOCTOU) gap allowed an attacker who could write to the workspace to atomically replace a project file with a symlink, causing Claude Code to follow the symlink and write its output to an arbitrary file outside the project sandbox. Exploitation required the ability to win a race condition against the write operation and write access to the shared workspace, enabling a lower-privileged attacker to redirect benign edits to sensitive files (e.g., shell configuration) in a higher-privileged session.\n\nUsers on standard Claude Code auto-update have received this fix already. Users performing manual updates are advised to update to the latest version.\n\nThank you to hackerone.com/c_h4ck_0 for reporting this issue.","dates":{"published":"2026-10-07T12:50:02.572Z","modified":"2026-10-07T14:39:13.225Z","reserved":null,"kevAdded":[],"kevDue":[]},"cvss":{"headline":{"score":7.7,"severity":"high","version":"4.0","versionLabel":"v4.0","source":"CVE.org","vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N","computed":false,"selection":"backend-summary"},"metrics":[{"version":"4.0","versionLabel":"v4.0","source":"CVE.org","score":7.7,"severity":"high","vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N","exploitability":null,"impact":null,"computed":false},{"version":"4.0","versionLabel":"v4.0","source":"NVD","score":7.7,"severity":"high","vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/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","exploitability":null,"impact":null,"computed":false}]},"epss":{"probability":0.00251,"percentile":0.15526,"severity":"low","asOf":"2026-10-22T00:00:00.000Z","change":{"pp":null,"baselineDate":null,"baselineScore":null},"history":[{"date":"2026-10-08T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-09T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-10T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-11T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-12T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-13T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-14T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-15T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-16T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-17T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-18T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-19T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-20T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-21T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-22T00:00:00.000Z","score":0.00251,"percentile":0.15526}],"last30":[{"date":"2026-10-08T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-09T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-10T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-11T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-12T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-13T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-14T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-15T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-16T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-17T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-18T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-19T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-20T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-21T00:00:00.000Z","score":0.00251,"percentile":null},{"date":"2026-10-22T00:00:00.000Z","score":0.00251,"percentile":0.15526}]},"kev":{"state":"not-listed","entries":[],"listedCount":0,"totalCatalogs":3,"catalogs":[{"source":"cisa","label":"CISA","listed":false,"entry":null},{"source":"enisa","label":"ENISA","listed":false,"entry":null},{"source":"circl","label":"CIRCL","listed":false,"entry":null}]},"ransomware":{"state":"none-recorded","sources":[]},"exploits":[],"exploitCount":0,"weaknesses":[{"id":"CWE-22","name":"Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')","description":"The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.","type":"weakness","status":"Stable","abstraction":"Base","likelihoodOfExploit":"High","url":"https://cwe.mitre.org/data/definitions/22.html"},{"id":"CWE-61","name":"UNIX Symbolic Link (Symlink) Following","description":"The product, when opening a file or directory, does not sufficiently account for when the file is a symbolic link that resolves to a target outside of the intended control sphere. This could allow an attacker to cause the product to operate on unauthorized files.","type":"weakness","status":"Incomplete","abstraction":"Compound","likelihoodOfExploit":"High","url":"https://cwe.mitre.org/data/definitions/61.html"},{"id":"CWE-367","name":"Time-of-check Time-of-use (TOCTOU) Race Condition","description":"The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check.","type":"weakness","status":"Incomplete","abstraction":"Base","likelihoodOfExploit":"Medium","url":"https://cwe.mitre.org/data/definitions/367.html"}],"affected":[{"vendor":"anthropic","product":"@anthropic-ai/claude-code","name":"@anthropic-ai/claude-code","label":"@anthropic-ai/claude-code","ecosystem":null,"cpePart":"a","purl":null,"purlType":null,"versions":[{"text":"< 2.1.129","noFixRecorded":false,"fixedIn":null}],"versionsText":"< 2.1.129","eol":null,"hubHref":"/vendor/anthropic/anthropic-aiclaude-code"}],"affectedCount":1,"eol":{"hasEol":false,"count":0},"references":[{"url":"https://github.com/anthropics/claude-code/security/advisories/GHSA-5j29-h97v-84ch","label":"github.com/anthropics/claude-code/security/advisories/GHSA-5j29-h97v-84ch","hostname":"github.com","tags":[]}],"lineage":{"upstream":[],"downstream":[],"duplicates":[],"related":[]},"timeline":[{"kind":"published","date":"2026-10-07T12:50:02.572Z","label":"Published","detail":"Vulnerability first disclosed.","source":null},{"kind":"modified","date":"2026-10-07T14:39:13.225Z","label":"Last modified","detail":"Vulnerability information updated.","source":null}],"risk":{"score":31,"level":"medium","profile":"Default","thresholds":{"critical":75,"high":50,"medium":25,"low":10}},"meta":{"dataAsOf":"2026-10-22T20:10:02.738Z","stale":false,"partial":false}}