CVE-2026-103435 Arbitrary File Write via Write-Time Symlink Following (TOCTOU) in Claude Code
An attacker with workspace write access can exploit a race condition to redirect file writes outside the sandbox, potentially escalating privileges or executing code.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-103435?
CVE-2026-103435 is a high-severity path traversal vulnerability in @anthropic-ai/claude-code, published on 7 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
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.
Which versions are affected by CVE-2026-103435?
How do I fix CVE-2026-103435?
No fix has been published for CVE-2026-103435 yet. Limit exposure of the affected software until one is available.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is CVE-2026-103435 being exploited?
There is no known exploitation of CVE-2026-103435 in the wild and no public exploit code.
Sources
Also known as GHSA-5j29-h97v-84ch.