Arbitrary File Write via Write-Time Symlink Following (TOCTOU) in Claude Code

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-103435
StatePUBLISHED
AssignerAnthropic
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-07 13:17:16 UTC
Updated2026-10-07 15:16:57 UTC
DescriptionClaude 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. Users on standard Claude Code auto-update have received this fix already. Users performing manual updates are advised to update to the latest version. Thank you to hackerone.com/c_h4ck_0 for reporting this issue.

Risk And Classification

Primary CVSS: v4.0 7.7 HIGH from 98a01053-8a31-4f6d-9aa9-252be161adc6

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

Problem Types: CWE-22 | CWE-61 | CWE-367 | CWE-22 CWE-22 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') | CWE-61 CWE-61 UNIX Symbolic Link (Symlink) Following | CWE-367 CWE-367 Time-of-check Time-of-use (TOCTOU) Race Condition

VersionSourceTypeScoreSeverityVector
4.098a01053-8a31-4f6d-9aa9-252be161adc6Secondary7.7HIGHCVSS: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/C...
4.0CNADECLARED7.7HIGHCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
Present
Privileges Required
None
User Interaction
Passive
Confidentiality
High
Integrity
High
Availability
High
Sub Conf.
None
Sub Integrity
None
Sub Availability
None

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Anthropic @anthropic-ai/claude-code affected 2.1.129 semver Not specified

References

ReferenceSourceLinkTags
github.com/anthropics/claude-code/security/advisories/GHSA-5j29-h97v-84ch 98a01053-8a31-4f6d-9aa9-252be161adc6 github.com
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