What’s Vulnerable › Vulnerabilities
CVE-2026-103435: Arbitrary File Write via Write-Time Symlink Following (TOCTOU) in Claude Code
- Severity: high (CVSS 7.7 v4.0)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.3% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-10-07 · updated 2026-10-07
- Weakness: CWE-22
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
- Anthropic @anthropic-ai/claude-code: before 2.1.129 — fixed in 2.1.129
How to fix
Upgrade to a fixed version: Anthropic @anthropic-ai/claude-code 2.1.129. Check the vendor advisory for mitigations.
References
Get alerted when CVE-2026-103435 or the next vulnerability affects your stack