Bug 2547427 (CVE-2026-103435)

Summary: CVE-2026-103435 claude-code: claude-code: Arbitrary file write via TOCTOU race condition
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: sdawley
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in claude-code. An attacker with write access to a shared workspace can achieve arbitrary file modification and privilege escalation by exploiting a time-of-check to time-of-use (TOCTOU) race condition. By replacing a project file with a symbolic link between the permission check and the write operation, an attacker can bypass workspace restrictions and overwrite sensitive files outside the project sandbox.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-10-07 13:02:52 UTC 
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.