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Fencer Intel
critical 9.8

CVE-2021-31921 json

Istio before 1.8.6 and 1.9.x before 1.9.5 contains a remotely exploitable vulnerability where an external client can access unexpected serv…

published 5y ago modified 4mo ago also EUVD-2021-18794

cvss
9.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.5%
EPSS 1.5% chance of exploitation in 30 days, percentile 73%
public exploits
0
none known

Summary

Istio before 1.8.6 and 1.9.x before 1.9.5 contains a remotely exploitable vulnerability where an external client can access unexpected services in the cluster, bypassing authorization checks, when a gateway is configured with AUTO_PASSTHROUGH routing configuration.

Patch / fix

  • istio istio 1.8.6, 1.9.5
  • servicemesh service mesh 1.1 1.1.15-4.el8
  • servicemesh-mixc service mesh 1.1 1.1.15-4.el8
  • servicemesh-mixs service mesh 1.1 1.1.15-4.el8
  • servicemesh-galley service mesh 1.1 1.1.15-4.el8
  • servicemesh-citadel service mesh 1.1 1.1.15-4.el8
  • servicemesh-istioctl service mesh 1.1 1.1.15-4.el8
  • servicemesh-pilot-agent service mesh 1.1 1.1.15-4.el8
  • servicemesh-pilot-discovery service mesh 1.1 1.1.15-4.el8

red hat advisories RHSA-2021:2085RHSA-2021:2061

  • istio Arch Linux 1.10.0-1

arch linux advisories AVG-1947

Is CVE-2021-31921 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

Check with Fencer

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-31921 updated cvss 10.0

istio/istio: authorization bypass when using AUTO_PASSTHROUGH

  • Red Hat OpenShift Service Mesh 1.1 servicemesh 1.1.15-4.el8, servicemesh-mixc 1.1.15-4.el8, servicemesh-mixs 1.1.15-4.el8, servicemesh-galley 1.1.15-4.el8, servicemesh-citadel 1.1.15-4.el8, servicemesh-istioctl 1.1.15-4.el8, +3 more
    fixed: vendor fix RHSA-2021:2085
  • Red Hat OpenShift Service Mesh 2.0 servicemesh 2.0.5-3.el8, servicemesh-mixc 2.0.5-3.el8, servicemesh-mixs 2.0.5-3.el8, servicemesh-istioctl 2.0.5-3.el8, servicemesh-pilot-agent 2.0.5-3.el8, servicemesh-pilot-discovery 2.0.5-3.el8
    fixed: vendor fix RHSA-2021:2061

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.45% chance of exploitation in the next 30 days, higher than 73% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • istio.io https://istio.io/latest/news/security/istio-security-2021-006/ referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 6.8 AV:N/AC:M/Au:N/C:P/I:P/A:P

Classification

Weakness

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.