Authorization Policy Bypass Due to Case Insensitive Host Comparison

CVE-2021-39155 → View on GitHub ↗ View on CVE.org ↗ View on NVD ↗

Description

Impact

According to RFC 4343, 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 Envoy 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

  • Istio 1.11.1 and above
  • Istio 1.10.4 and above
  • Istio 1.9.8 and above

Workarounds

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 guide.

References

More details can be found in the Istio Security Bulletin.

For more information

If you have any questions or comments about this advisory, please email us at [email protected]

Basic information

Type
reviewed
Severity
high
Advisory on GitHub
Open advisory ↗
Repository advisory
Open repository advisory ↗
Source code
Browse source ↗
Published (advisory)
2021-08-30 16:15:56 UTC
Updated
2023-05-22 18:26:48 UTC
GitHub reviewed
2021-08-25 22:29:16 UTC
NVD published
2021-08-24

EPSS Score

Score Percentile
0.17% 38.47%

CVSS Scores

Base score Version Severity Vector
8.3 3.1 —
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:L Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:L)
Might cause slowdowns, glitches, or partial disruption—not a full brick.

Identifiers

Type Value
GHSA GHSA-7774-7vr3-cc8j ↗
CVE CVE-2021-39155 ↗

CWEs

CWE id Name
CWE-178 Improper Handling of Case Sensitivity

Credits

  • yangminzhu (analyst)
  • avivdolev (analyst)
  • tdunlap607 (analyst)

Affected packages (3)

Vulnerable version ranges and first patched releases as published by GitHub.

Ecosystem Package Vulnerable range First patched Vulnerable functions
go istio.io/istio < 1.9.8 1.9.8 —
go istio.io/istio >= 1.10.0, < 1.10.4 1.10.4 —
go istio.io/istio = 1.11.0 1.11.1 —

References

cvelogic Threat Intelligence