GHSA-w828-4qhx-vxx3 CVE-2026-34452 PYSEC-2026-2115
Claude SDK for Python: Memory Tool Path Validation Race Condition Allows Sandbox Escape
- Severity
- 5.8 / 10
- Medium · CVSS 4.0
- Exploit chance (EPSS)
- 0.14%
- Chance of exploitation in the next 30 days. Higher than 3.65% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-59 Improper Link Resolution Before File Access ('Link Following')
- CWE-367 Time-of-check Time-of-use (TOCTOU) Race Condition
- Fix
0.87.0- Upgrade anthropic to this version or later
Description
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.
Users on the affected versions are advised to update to the latest version.
Claude SDK for Python thanks hackerone.com/kasthelord for reporting this issue!
Affected versions
PyPI
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
anthropic PyPI → 0.87.0
- pip
pip install --upgrade "anthropic>=0.87.0"- poetry
poetry add "anthropic>=0.87.0"- uv
uv add "anthropic>=0.87.0"
Severity breakdown
CVSS 4.0 5.8
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
- Attack vector
- Local
- Attack complexity
- High
- Attack requirements
- None
- Privileges required
- Low
- User interaction
- None
- Confidentiality (vulnerable system)
- High
- Integrity (vulnerable system)
- Low
- Availability (vulnerable system)
- None
- Confidentiality (subsequent systems)
- None
- Integrity (subsequent systems)
- None
- Availability (subsequent systems)
- None
CVSS 3.1 5.3
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:N
- Attack vector
- Local
- Attack complexity
- High
- Privileges required
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- Low
- Availability
- None
Weakness
CWE-59: Improper Link Resolution Before File Access ('Link Following')
The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.
How to prevent it
- Architecture and Design: Follow the principle of least privilege when assigning access rights to entities in a software system. Denying access to a file can prevent an attacker from replacing that file with a link to a sensitive file. Ensure good compartmentalization in the system to provide protected areas that can be trusted.
CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition
The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check.
How to prevent it
- Implementation: The most basic advice for TOCTOU vulnerabilities is to not perform a check before the use. This does not resolve the underlying issue of the execution of a function on a resource whose state and identity cannot be assured, but it does help to limit the false sense of security given by the check.
- Implementation: When the file being altered is owned by the current user and group, set the effective gid and uid to that of the current user and group when executing this statement.
- Architecture and Design: Limit the interleaving of operations on files from multiple processes.
- Implementation, Architecture and Design: If you cannot perform operations atomically and you must share access to the resource between multiple processes or threads, then try to limit the amount of time (CPU cycles) between the check and use of the resource. This will not fix the problem, but it could make it more difficult for an attack to succeed.
- Implementation: Recheck the resource after the use call to verify that the action was taken appropriately.
- Architecture and Design: Ensure that some environmental locking mechanism can be used to protect resources effectively.
- Implementation: Ensure that locking occurs before the check, as opposed to afterwards, such that the resource, as checked, is the same as it is when in use.
References
Advisories
Fixes and patches
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-q5f5-3gjm-7mfm Claude SDK for Python has Insecure Default File Permissions in Local Filesystem Memory Tool | Medium | Also affects anthropic |
| GHSA-hjqx-j4rw-g7xv zip: Arbitrary file write outside the extraction directory, because ZipArchive::extract validates symlink targets lexically. | High | Same weakness, CWE-59 |
| GHSA-4vjg-vx72-qq4g systeminformation has path traversal in Linux networkStats() that allows symlink-based file disclosure outside /sys/class/net | Low | Same weakness, CWE-59 |
| GHSA-9j6q-wvj5-jgjg filelock: Symlink swap during SoftFileLock's writability check leaks whether a path exists and is writable by the lock taker | Low | Same weakness, CWE-59 |
| GHSA-j8f7-rjxc-mr56 filelock: ReadWriteLock follows a symlink at the lock path into SQLite | Medium | Same weakness, CWE-59 |
| GHSA-crv4-6mhj-j5jh filelock: SoftFileLock stale-break restore follows a swapped-in symbolic link and hard-links a file of the user running the lock into the lock directory | Medium | Same weakness, CWE-59 |
| GHSA-v4x8-3wr5-3wq8 filelock ReadWriteLock: SQLite reopens the lock database by name, so a planted symlink or journal file makes the lock user's process overwrite or unlink its own files | High | Same weakness, CWE-59 |
| GHSA-gq48-pqfc-9p58 GitPython: Submodule.move() follows an attacker-committed intermediate symlink outside the worktree | Medium | Same weakness, CWE-59 |
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