Vulnerability · Published Oct 7, 2026 · Assigned by Anthropic
CVE-2026-103435Arbitrary File Write via Write-Time Symlink Following (TOCTOU) in Claude Code
High 7.7
In plain English
A high-severity path traversal in @anthropic-ai/claude-code from Anthropic. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 17% of all known vulnerabilities).
Official 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. 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.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Anthropic | @anthropic-ai/claude-code | 0 – before 2.1.129 |
Weakness: CWE-22, CWE-61, CWE-367 · 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