Is CVE-2026-91403 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-91403 being exploited in the wild.

How severe is CVE-2026-91403?

High severity, published 21 October 2026.

Which products and versions are affected?

rustls-webpki (crates.io) SEMVER:introduced=0.0.0-0,fixed=0.103.16,introduced=0.104.0-alpha.1,fixed=0.104.0-alpha.8; webpki-root-certs (crates.io) SEMVER:introduced=0.0.0-0,fixed=0.26.11,introduced=0.26.12-0,fixed=1.0.10; webpki-roots (crates.io) SEMVER:introduced=0.0.0-0,fixed=0.26.11,introduced=0.26.12-0,fixed=1.0.10; stdlib (Go) SEMVER:introduced=0,fixed=1.26.10,introduced=1.27.0-0,fixed=1.27.3; and 1 more.

Is there a fix for CVE-2026-91403?

Yes. rustls-webpki (crates.io): upgrade to 0.104.0-alpha.8 or later; webpki-root-certs (crates.io): upgrade to 1.0.10 or later; webpki-roots (crates.io): upgrade to 1.0.10 or later; stdlib (Go): upgrade to 1.27.3 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-91403 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-91403?

Check whether you run Amazon AWS, rustls-webpki (crates.io), webpki-root-certs (crates.io) or one of the others listed 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.

CVE-2026-91403: Go crypto/x509 untrusted intermediate certificate validation

CVE-2026-91403 · Severity: high · Published 2026-10-21

Go's crypto/x509 library uses system root certificates on most platforms, but in some cases these trust stores may not be updated. Go has added a denylist that blocks verification of intermediate certificates known to no longer be trustworthy, preventing the use of compromised or revoked signing certificates in applications built with Go.

Technologies: Amazon AWS, rustls-webpki (crates.io), stdlib (Go), Google Go, Google Cloud Platform. Vendors: Amazon, crates.io, Go, Google.

Quick answers

Is CVE-2026-91403 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-91403 being exploited in the wild.
How severe is CVE-2026-91403?: High severity, published 21 October 2026.
Which products and versions are affected?: rustls-webpki (crates.io) SEMVER:introduced=0.0.0-0,fixed=0.103.16,introduced=0.104.0-alpha.1,fixed=0.104.0-alpha.8; webpki-root-certs (crates.io) SEMVER:introduced=0.0.0-0,fixed=0.26.11,introduced=0.26.12-0,fixed=1.0.10; webpki-roots (crates.io) SEMVER:introduced=0.0.0-0,fixed=0.26.11,introduced=0.26.12-0,fixed=1.0.10; stdlib (Go) SEMVER:introduced=0,fixed=1.26.10,introduced=1.27.0-0,fixed=1.27.3; and 1 more.
Is there a fix for CVE-2026-91403?: Yes. rustls-webpki (crates.io): upgrade to 0.104.0-alpha.8 or later; webpki-root-certs (crates.io): upgrade to 1.0.10 or later; webpki-roots (crates.io): upgrade to 1.0.10 or later; stdlib (Go): upgrade to 1.27.3 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-91403 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-91403?: Check whether you run Amazon AWS, rustls-webpki (crates.io), webpki-root-certs (crates.io) or one of the others listed 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

rustls-webpki (crates.io): upgrade to 0.104.0-alpha.8 or later
```
cargo update -p rustls-webpki
```
webpki-root-certs (crates.io): upgrade to 1.0.10 or later
```
cargo update -p webpki-root-certs
```
webpki-roots (crates.io): upgrade to 1.0.10 or later
```
cargo update -p webpki-roots
```
stdlib (Go): upgrade to 1.27.3 or later
```
go get stdlib@v1.27.3
```

Technical details

A denylist mechanism was implemented in Go's crypto/x509 package to reject known intermediate certificates during the Verify function call, addressing cases where system trust stores may not reflect the latest revocations. The vulnerability affects X.509 certificate verification on platforms where system root certificate updates may not be current, requiring an explicit denylist as a defense. This is a defensive security control rather than an exploitable vulnerability in the traditional sense.

Affected products

Google Go unspecified

Identifiers

CVE-2026-91403
CVE-2026-111943
GO-2026-6809
RUSTSEC-2026-0381
RUSTSEC-2026-0382
RUSTSEC-2026-0383

Timeline

2026-10-21: disclosed

References

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