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Fencer Vulns
high 8.1

CVE-2021-39156 json

Fragments in Path May Lead to Authorization Policy Bypass

published 2021-08-24 5 y ago modified 2026-09-10 1 mo ago also GHSA-hqxw-mm44-gc4r , EUVD-2021-1754

cvss
8.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.2%
EPSS 1.2% chance of exploitation in 30 days, percentile 67%
public exploits
0
none known

Summary

Istio is an open source platform for providing a uniform way to integrate microservices, manage traffic flow across microservices, enforce policies and aggregate telemetry data. Istio 1.11.0, 1.10.3 and below, and 1.9.7 and below contain a remotely exploitable vulnerability where an HTTP request with `#fragment` in the path may bypass Istio’s URI path based authorization policies. Patches are available in Istio 1.11.1, Istio 1.10.4 and Istio 1.9.8. As a work around a Lua filter may be written to normalize the path.

Patch / fix

  • go istio.io/istio 1.9.8, 1.10.4, 1.11.1
  • istio istio 1.9.8, 1.10.3, 1.11.1
  • servicemesh service mesh 1.1 1.1.17-3.el8
  • servicemesh-mixc service mesh 1.1 1.1.17-3.el8
  • servicemesh-mixs service mesh 1.1 1.1.17-3.el8
  • servicemesh-proxy service mesh 1.1 1.1.17-2.el8
  • servicemesh-galley service mesh 1.1 1.1.17-3.el8
  • servicemesh-citadel service mesh 1.1 1.1.17-3.el8
  • servicemesh-istioctl service mesh 1.1 1.1.17-3.el8
  • servicemesh-pilot-agent service mesh 1.1 1.1.17-3.el8

red hat advisories RHSA-2021:3273RHSA-2021:3272

  • istio Arch Linux 1.11.1-1

arch linux advisories AVG-2321

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-2021-39156 updated cvss 8.3

istio/istio: HTTP request with fragment in URI can bypass authorization mechanisms

  • Red Hat OpenShift Service Mesh 1.1 servicemesh 1.1.17-3.el8, servicemesh-mixc 1.1.17-3.el8, servicemesh-mixs 1.1.17-3.el8, servicemesh-galley 1.1.17-3.el8, servicemesh-citadel 1.1.17-3.el8, servicemesh-istioctl 1.1.17-3.el8, +3 more
    fixed: vendor fix RHSA-2021:3273
  • Red Hat OpenShift Service Mesh 2.0 servicemesh 2.0.7-3.el8, servicemesh-mixc 2.0.7-3.el8, servicemesh-mixs 2.0.7-3.el8, servicemesh-istioctl 2.0.7-3.el8, servicemesh-pilot-agent 2.0.7-3.el8, servicemesh-pilot-discovery 2.0.7-3.el8
    fixed: vendor fix RHSA-2021:3272
  • Red Hat OpenShift Service Mesh 1.1 servicemesh-proxy 1.1.17-2.el8 Red Hat OpenShift Service Mesh 2.0 servicemesh-proxy 2.0.7-3.el8
    not affected: vulnerable code not present

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

1.18% chance of exploitation in the next 30 days, higher than 67% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 8.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:P/I:N/A:N
GitHub 3.1 8.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

Affected packages

ecosystem package affected fixed in
go istio.io/istio
<1.9.8
>=1.10.0, <1.10.4
>=1.11.0, <1.11.1
1.9.8
1.10.4
1.11.1

Affected products

  • istio istio

Classification

Weakness
  • CWE-863 Incorrect Authorization
  • CWE-706 Use of Incorrectly-Resolved Name or Reference

References

Sources

Fencer Vulns 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.