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.
Published 2021-08-24 23:15:07
Updated 2024-02-21 21:01:31
Source GitHub, Inc.
View at NVD,   CVE.org

Exploit prediction scoring system (EPSS) score for CVE-2021-39155

0.14%
Probability of exploitation activity in the next 30 days EPSS Score History
~ 49 %
Percentile, the proportion of vulnerabilities that are scored at or less

CVSS scores for CVE-2021-39155

Base Score Base Severity CVSS Vector Exploitability Score Impact Score Score Source First Seen
5.0
MEDIUM AV:N/AC:L/Au:N/C:P/I:N/A:N
10.0
2.9
NIST
7.5
HIGH CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
3.9
3.6
NIST
8.3
HIGH CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:L
2.8
5.5
GitHub, Inc.

CWE ids for CVE-2021-39155

  • The product does not properly account for differences in case sensitivity when accessing or determining the properties of a resource, leading to inconsistent results.
    Assigned by:
    • nvd@nist.gov (Primary)
    • security-advisories@github.com (Secondary)
  • The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check. This allows attackers to bypass intended access restrictions.
    Assigned by: nvd@nist.gov (Primary)

References for CVE-2021-39155

Products affected by CVE-2021-39155

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