CVE-2021-39155
Authorization Policy Bypass Due to Case Insensitive Host Comparison
- Published
- Updated
- Reserved
- Assigned by
- GitHub_M
Description
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.
Timeline
ID reserved
By GitHub_M
- 8 days later
· 8 days later
Published
- 3 years later
· 3 years later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_MCNA (assigner) | 3.1 | High8.3 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:L |
| NVDNVD · Modified | 3.1 | High7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N |
- EPSS (exploitation in 30 days)
- 1.2% · top 31% of all CVEs (7 Nov 2026)
The list uses the assigner's score when there is one, then CISA's, then NVD's: High 8.3.
Weakness
Affected products
Affected packages
From reviewed advisories of the GitHub Advisory Database.
- Goistio.io/istioGHSA-7774-7vr3-cc8j (opens in a new tab)
References (2)
- https://github.com/istio/istio/security/advisories/GHSA-7774-7vr3-cc8j (opens in a new tab)x_refsource_CONFIRMx_transferred
- https://datatracker.ietf.org/doc/html/rfc4343 (opens in a new tab)x_refsource_MISCx_transferred
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisory GHSA-7774-7vr3-cc8j (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://trackcve.app/cve/CVE-2021-39155)Record last updated .