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CVE-2026-103435— Arbitrary File Write via Write-Time Symlink Following (TOCTOU) in Claude Code

Quick assessment

Affected
Anthropic @anthropic-ai/claude-code
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Claude Code 在权限检查阶段确认了目标文件路径位于项目工作目录内，但在执行写入操作时再次解析了路径，且未重复进行该权限验证。这种检查时间与使用时间的间隙（TOCTOU）漏洞使得能够在工作区中写入文件的攻击者能够原子地将项目文件替换为符号链接，从而导致 Claude Code 跟随符号链接，将输出写入到项目沙箱之外的任意文件。利用该漏洞需要能够与写入操作竞争获胜，并拥有对共享工作区的写入权限，从而使低权限攻击者能够将无害的编辑重定向到高权限会话中的敏感文件（例如 Shell 配置文件）。 已启用自动更新的

CVSS 7.7 · High
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I. Basic Information for CVE-2026-103435

Vulnerability Information
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Vulnerability Title
Arbitrary File Write via Write-Time Symlink Following (TOCTOU) in Claude Code
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
对路径名的限制不恰当(路径遍历)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Anthropic @anthropic-ai/claude-code 0 ~ 2.1.129 -

II. Public POCs for CVE-2026-103435

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III. Intelligence Information for CVE-2026-103435

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Other References for CVE-2026-103435 (1)

IV. Related Vulnerabilities

Same product: @anthropic-ai/claude-code
Same vendor: Anthropic
Same weakness: CWE-22

V. Comments for CVE-2026-103435

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