CVE-2021-39155

HIGHNVD 8.38.3—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 8.3 under NVD CVSS v3. EPSS exploit probability: 1.2%, top 36% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
Trending — 3 sources updated this week
8.3
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 1%CVSS: 8.3Exploit: NoneExposed: 0

A fix is available — apply it.

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, 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 guide.

CVSS v3
8.3
EG Score
8.3(medium)
EG Risk
—
EPSS
64.3%
KEV
Not listed

Published

August 24, 2021

Last Modified

November 21, 2024

References (4)

Patch Availability(2)

Vendor / EcosystemFixed in / PatchReleasedSource
redhatservicemesh-0:1.1.17-3.el82021-08-25redhat
redhatservicemesh-0:2.0.7-3.el82021-08-25redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(1 across 1 ecosystem)
Go(1)
PackageVulnerable rangeFixed inDependents
istio.io/istio1.11.01.11.1—

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

All Vendor Advisories

(2)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 14× in last 7d / 45× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 101 total refreshes for this CVE.

  1. 2026-07-22 22:50 UTCEG score recompute
  2. 2026-07-22 14:06 UTCEPSS rescore
  3. 2026-07-22 14:06 UTCEPSS rescore
  4. 2026-07-21 15:22 UTCEPSS rescore
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  10. 2026-07-18 13:29 UTCOSV refresh
  11. 2026-07-18 10:02 UTCEPSS rescore
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  24. 2026-07-08 15:12 UTCEPSS rescore
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  1. 2026-07-06 16:25 UTCEPSS rescore
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  8. 2026-06-30 23:20 UTCEPSS rescore
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  10. 2026-06-30 17:00 UTCOSV refresh
  11. 2026-06-28 14:05 UTCEPSS rescore
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  23. 2026-06-21 14:55 UTCEPSS rescore
  24. 2026-06-21 01:58 UTCEPSS rescore
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  26. 2026-06-19 19:24 UTCEPSS rescore
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  28. 2026-06-18 17:51 UTCEPSS rescore
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  35. 2026-06-13 22:58 UTCEPSS rescore
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  37. 2026-06-12 23:37 UTCOSV refresh
  38. 2026-06-12 23:10 UTCEPSS rescore
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  40. 2026-06-11 13:58 UTCEPSS rescore
  41. 2026-06-10 22:16 UTCEPSS rescore
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  43. 2026-06-08 14:15 UTCEPSS rescore
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  45. 2026-06-07 15:23 UTCEPSS rescore
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  47. 2026-06-06 13:46 UTCEPSS rescore
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  50. 2026-06-05 22:45 UTCEPSS rescore
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  70. 2026-05-26 13:42 UTCEPSS rescore
  71. 2026-05-26 11:29 UTCEG score recompute
  72. 2026-05-26 11:29 UTCVendor advisory
  73. 2026-05-26 07:17 UTCEPSS rescore
  74. 2026-05-26 07:17 UTCEPSS rescore
  75. 2026-05-26 07:17 UTCEPSS rescore

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Frequently asked(5)

What is CVE-2021-39155?
CVE-2021-39155 is a high vulnerability published on August 24, 2021. 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, Istio authorization policy should compare the hostname in the HTTP Host header in a case…
When was CVE-2021-39155 disclosed?
CVE-2021-39155 was first published in the National Vulnerability Database on August 24, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-39155 actively exploited?
CVE-2021-39155 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 64.3% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-39155?
CVE-2021-39155 has a CVSS v3 base score of 8.3 (NVD).
How do I remediate CVE-2021-39155?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-39155, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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