Is This vulnerability exploited in the wild?

No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.

How severe is This vulnerability?

Critical severity, with a CVSS score of 4, published 20 October 2026.

Which products and versions are affected?

Astral Uv before 0.13.4; uv (PyPI) < 0.13.4, ECOSYSTEM:introduced=0,fixed=0.13.4.

How is This vulnerability attacked?

It is attacked over the network.

Check whether you run Astral Uv or uv (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

uv bundled CA store trusts compromised emSign root

Q: Is there a fix for This vulnerability?

Yes. uv (PyPI): upgrade to 0.13.4 or later. Until then: Users can work around the vulnerability without upgrading by using system certificates (--system-certs flag) or custom certificates (SSL_CERT_FILE or SSL_CERT_DIR environment variables) that do not contain the compromised intermediates or emSign roots. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

Q: How is This vulnerability attacked?

It is attacked over the network.

Q: Am I affected?

Check whether you run Astral Uv or uv (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Severity: critical · CVSS 4 · Published 2026-10-20

uv is a Python package manager that verifies secure connections using a bundled list of trusted certificate authorities. An emSign root certificate authority whose intermediate signing keys have been compromised is included in uv's default certificate store, allowing attackers with those compromised keys to impersonate any website and intercept encrypted connections. Upgrading to uv 0.13.4 or later removes the compromised root from the bundle.

Technologies: Astral Uv, uv (PyPI). Vendors: Astral, PyPI.

Quick answers

Is This vulnerability exploited in the wild?: No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.
How severe is This vulnerability?: Critical severity, with a CVSS score of 4, published 20 October 2026.
Which products and versions are affected?: Astral Uv before 0.13.4; uv (PyPI) < 0.13.4, ECOSYSTEM:introduced=0,fixed=0.13.4.
Is there a fix for This vulnerability?: Yes. uv (PyPI): upgrade to 0.13.4 or later. Until then: Users can work around the vulnerability without upgrading by using system certificates (--system-certs flag) or custom certificates (SSL_CERT_FILE or SSL_CERT_DIR environment variables) that do not contain the compromised intermediates or emSign roots. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is This vulnerability attacked?: It is attacked over the network.
Am I affected?: Check whether you run Astral Uv or uv (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

uv (PyPI): upgrade to 0.13.4 or later
```
pip install "uv>=0.13.4"
```

Users can work around the vulnerability without upgrading by using system certificates (--system-certs flag) or custom certificates (SSL_CERT_FILE or SSL_CERT_DIR environment variables) that do not contain the compromised intermediates or emSign roots.

Technical details

uv versions before 0.13.4 include the emSign ECC Root CA - G3 root in their vendored webpki-root-certs bundle. Eight eMudhra intermediate certificates chaining to this root have had their private keys compromised and revoked by the CA. An attacker possessing one of these compromised intermediate keys can issue valid certificates for any hostname that uv will accept, enabling man-in-the-middle attacks on TLS connections. The fix removes the root entirely from the bundled certificate store.

Affected products

Astral uv before 0.13.4

Identifiers

GHSA-hq85-5cpj-mr62
PYSEC-2026-4321

Timeline

2026-10-20: disclosed
2026-10-20: patched: uv 0.13.4 released

References

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