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TI-2021-16541 Aliases CVE-2021-39155GHSA-7774-7vr3-cc8j

Authorization Policy Bypass Due to Case Insensitive Host Comparison

Priority LOW 39CWE-178Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
Required
Attack complexity
Low
Impact type
Security bypass
Confidentiality · integrity · availability
High · High · Low
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA, GitHub and Red Hat. Impact type from CWE-863.

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. According to [RFC 4343](https://datatracker.ietf.org/doc/html/rfc4343), Istio authorization policy should compare the hostname in the HTTP Host header in a case insensitive way, but currently the comparison is case sensitive. The proxy will route the request hostname in a case-insensitive way which means the authorization policy could be bypassed. As an example, the user may have an authorization policy that rejects request with hostname "httpbin.foo" for some source IPs, but the attacker can bypass this by sending the request with hostname "Httpbin.Foo". 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 Host header before the authorization check. This is similar to the Path normalization presented in the [Security Best Practices](https://istio.io/latest/docs/ops/best-practices/security/#case-normalization) guide.

Why it matters now

EPSS 0.01242 69th percentileScored 2026-11-07
Fix Fixed istio (istio): 1.10.4, 1.11.1istio.io/istio (Go): 1.9.8, 1.10.4, 1.11.1Red Hat: 2 advisories

SSVC decision points

Not available: CISA has not published SSVC decision points for this record.

Affected products

VendorProductAffected versionsFixed inStatusSource
istioistioup to 1.9.8; 1.10.0 to before 1.10.4; 1.11.0 to before 1.11.11.10.4, 1.11.1Patch availableCNA
—istio.io/istio (Go)before 1.9.81.9.8Patch availableGHSA-7774-7vr3-cc8j
—istio.io/istio (Go)1.10.0 to before 1.10.41.10.4Patch availableGHSA-7774-7vr3-cc8j
—istio.io/istio (Go)1.11.0 to before 1.11.11.11.1Patch availableGHSA-7774-7vr3-cc8j
  • istio Vendoristio Affected up to 1.9.8; 1.10.0 to before 1.10.4; 1.11.0 to before 1.11.1 Fixed in 1.10.4, 1.11.1 Patch available CNA
  • istio.io/istio (Go) Vendor— Affected before 1.9.8 Fixed in 1.9.8 Patch available GHSA-7774-7vr3-cc8j
  • istio.io/istio (Go) Vendor— Affected 1.10.0 to before 1.10.4 Fixed in 1.10.4 Patch available GHSA-7774-7vr3-cc8j
  • istio.io/istio (Go) Vendor— Affected 1.11.0 to before 1.11.1 Fixed in 1.11.1 Patch available GHSA-7774-7vr3-cc8j

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:istio:istio:*:*:*:*:*:*:*:*before 1.9.8; 1.10.0 to before 1.10.4; 1.11.0 to before 1.11.1Vulnerableistio
  • cpe:2.3:a:istio:istio:*:*:*:*:*:*:*:* Versions before 1.9.8; 1.10.0 to before 1.10.4; 1.11.0 to before 1.11.1 Vulnerable ·istio

Remediation

  • Fix · CNA istio (istio) Fixed in 1.10.4, 1.11.1
  • Fix · GHSA-7774-7vr3-cc8j istio.io/istio (Go) Fixed in 1.9.8 Advisory →
  • Fix · GHSA-7774-7vr3-cc8j istio.io/istio (Go) Fixed in 1.10.4 Advisory →
  • Fix · GHSA-7774-7vr3-cc8j istio.io/istio (Go) Fixed in 1.11.1 Advisory →

Red Hat 2 advisories

  • RHSA-2021:3272 Released 2021-08-25 · Red Hat rating Important
    Red Hat OpenShift Service Mesh 2.0.7.1 security update
    • OpenShift Service Mesh 2.0 servicemesh-2.0.7-3.el8, servicemesh-istioctl-2.0.7-3.el8, servicemesh-mixc-2.0.7-3.el8 +4
  • RHSA-2021:3273 Released 2021-08-25 · Red Hat rating Important
    Red Hat OpenShift Service Mesh 1.1.17.1 security update
    • OpenShift Service Mesh 1.1 servicemesh-1.1.17-3.el8, servicemesh-citadel-1.1.17-3.el8, servicemesh-galley-1.1.17-3.el8 +7

Vendor assessments

Red Hat

Red Hat rating: Important. Red Hat's page for this CVE →

ProductStatusPlan or fix
OpenShift Service Mesh 1.1Fixed RHSA-2021:3273
OpenShift Service Mesh 2.0Fixed RHSA-2021:3272
Not affected: 2 products
  • OpenShift Service Mesh 1.1
  • OpenShift Service Mesh 2.0

Timeline

  1. 2026-10-02 Threatist record created from CVE-2021-39155
  2. 2026-10-03 Alias added: GHSA-7774-7vr3-cc8j

References

Advisory 3

Other 4

  • TI-2026-79288 Out-of-bounds write in Google Brotli decoder KEVCVSS 4.0CRITICAL 9.2
  • TI-2023-23979 The HTTP/2 protocol allows a denial of service (server resource consumption) because… KEVCVSS 3.1HIGH 7.5
  • TI-2022-06055 Authorization Policy bypass in Istio CVSS 3.1CRITICAL 9.8
  • TI-2021-11909 Istio before 1.8.6 and 1.9.x before 1.9.5 contains a remotely exploitable vulnerability… CVSS 3.1CRITICAL 9.8
  • TI-2026-24390 Istio JWKS resolver to prevent private key material from being exposed when JWKS fetch fails. CVSS 4.0HIGH 8.7
  • TI-2022-13090 Ill-formed headers may lead to unexpected behavior in Istio CVSS 3.1CRITICAL 9.8
See all 28 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences