EUVD-2026-17681
GHSA-w828-4qhx-vxx3
Severity by source
CVSS:4.0/AV:L/AC:H/AT:N/PR:L/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Primary rating from GitHub Advisory · only source for this CVE.
CVSS VectorGitHub Advisory
CVSS:4.0/AV:L/AC:H/AT:N/PR:L/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Lifecycle Timeline
4Blast Radius
ecosystem impact- 11 pypi packages depend on anthropic (8 direct, 3 indirect)
Ecosystem-wide dependent count for version 0.86.0.
DescriptionGitHub Advisory
The Claude SDK for Python provides access to the Claude API from Python applications. From version 0.86.0 to before version 0.87.0, the async local filesystem memory tool in the Anthropic Python SDK validated that model-supplied paths resolved inside the sandboxed memory directory, but then returned the unresolved path for subsequent file operations. A local attacker able to write to the memory directory could retarget a symlink between validation and use, causing reads or writes to escape the sandbox. The synchronous memory tool implementation was not affected. This issue has been patched in version 0.87.0.
AnalysisAI
Symlink race condition in Anthropic Python SDK async filesystem memory tool (versions 0.86.0-0.86.x) allows local authenticated attackers to escape sandbox restrictions and read or write arbitrary files outside the designated memory directory. The vulnerability exploits a time-of-check-time-of-use (TOCTOU) flaw where path validation occurs before symlink resolution, enabling an attacker with memory directory write access to redirect file operations via symlink manipulation. The synchronous implementation is unaffected. Vendor-released patch: version 0.87.0.
Technical ContextAI
The Anthropic Python SDK implements local filesystem memory tools to provide sandboxed file access for Claude API applications. The async variant validates that model-supplied file paths resolve within a designated memory directory sandbox, but critically passes the unresolved path to subsequent file operations rather than the canonicalized result. This creates a classic TOCTOU race condition (CWE-59) where a local attacker with write permissions to the memory directory can modify symlinks between the validation check and actual file I/O. An attacker exploiting this can craft symlinks that pass validation (pointing inside the sandbox) but are retargeted to arbitrary locations before the file operation executes, bypassing all sandbox enforcement. The synchronous implementation avoids this issue by likely using resolved paths for operations.
RemediationAI
Upgrade Anthropic Python SDK to version 0.87.0 or later immediately. The patch resolves the vulnerability by properly resolving symlinks before performing file operations, eliminating the TOCTOU window. Users unable to upgrade immediately should restrict write permissions on the memory directory to the application process only, preventing untrusted local users from creating or modifying symlinks. The fix is included in the released version 0.87.0 available on PyPI; apply via pip install --upgrade anthropic>=0.87.0. Reference commit 6599043eee6e86dce16953fcd1fd828052052be6 in the upstream repository for implementation details.
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External POC / Exploit Code
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