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CPython tarfile CVE-2026-11940

| EUVDEUVD-2026-38490 HIGH
Path Traversal (CWE-22)
2026-06-23 PSF GHSA-9mc4-rqmq-h467
Path Traversal Cpython
7.8
CVSS 4.0 · Vendor: PSF
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Severity by source

Vendor (PSF) PRIMARY
7.8 HIGH
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/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
vuln.today AI
8.2 HIGH

Requires a victim app to extract an attacker-supplied archive (UI:R, AV:L for archive-as-input); scope changes to filesystem outside dest (S:C) enabling arbitrary read/write.

3.1 AV:L/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
4.0 AV:L/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N
SUSE
9.8 CRITICAL
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Primary rating from Vendor (PSF).

CVSS VectorVendor: PSF

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/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
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

2
Source Code Evidence Fetched
Jun 23, 2026 - 17:01 vuln.today
Analysis Generated
Jun 23, 2026 - 17:01 vuln.today

DescriptionCVE.org

tarfile.extractall() with the 'data' or 'tar' filter could be bypassed by a crafted archive where a hardlink references a symlink stored at a deeper name than the hardlink itself. The extraction fallback validated the symlink at it's archived location but recreated it at the hardlink's shallower path, letting a relative target the filter judged contained escape the destination directory. This allowed a malicious tar archive to create a symlink pointing outside the destination, enabling out-of-destination file reads or writes. This was an incomplete fix of CVE-2025-4330.

AnalysisAI

Path traversal in CPython's tarfile module allows a crafted tar archive to bypass the 'data' and 'tar' extraction filters and create a symlink pointing outside the destination directory, enabling out-of-destination file reads or writes when extractall() is later used or the resulting symlink is followed. The flaw is an incomplete fix of CVE-2025-4330: a hardlink referencing a symlink stored at a deeper path than the hardlink itself causes the fallback to validate the symlink at its archived (deep) location but recreate it at the hardlink's shallower path, making a previously 'contained' relative target escape the extraction root. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Craft tar with deep symlink and shallow hardlink
Delivery
Deliver archive to victim service
Exploit
Victim calls extractall with 'data' filter
Execution
Fallback recreates symlink at shallow path
Persist
Symlink escapes destination directory
Impact
Subsequent file op reads or writes outside dest
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Vulnerability AssessmentAI

Exploitation Exploitation requires a victim Python application to call tarfile.extractall() (or the equivalent TarFile.extract loop) with filter='data' or filter='tar' on an attacker-supplied archive, and the host must support symlink creation for the malicious link to materialize (the test skips when os_helper.can_symlink() is false). … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment Signals are mixed and worth disentangling. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker uploads a crafted .tar.gz to a service that later calls tarfile.extractall(path=dest, filter='data') - for example a CI artifact processor, plugin installer, or ML model importer. The archive contains a symlink at a/b/s -> ../escape and a hardlink at s pointing to a/b/s; after extraction, s becomes a symlink to ../escape that resolves outside dest, so any subsequent open() or write() through that path reads or overwrites files outside the intended directory. …
Remediation Upstream fix available (PR/commit); released patched version not independently confirmed - apply the CPython update that incorporates pull request https://github.com/python/cpython/pull/151559 as soon as your distribution publishes it, and consult the PSF advisory at https://mail.python.org/archives/list/security-announce@python.org/thread/LD6QIISNQFQYOIEPJNEUIPV7S3V76FZH/ for the exact patched minor versions. … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours: Identify all systems running CPython and using tarfile for archive extraction, particularly those processing archives from external or untrusted sources. …

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CVE-2026-11940 vulnerability details – vuln.today
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