CVE-2026-31837Network attack vector

Unauthenticated JWT forgery via fallback default keys

Published Mar 10, 2026 · Updated Mar 10, 2026

Authentication bypass in affected Istio releases allows remote attackers to forge accepted JWTs after a JWKS fetch failure. When JWKS retrieval fails, istiod falls back to publicly known default keys, causing JWT verification to accept attacker-forged tokens. Direct exposure requires a RequestAuthentication resource configured with jwksUri and grants unauthorized access to resources protected by JWT authentication.

CVSS severity8.7
High
EPSS probability0.38%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in affected Istio releases allows remote attackers to forge accepted JWTs after a JWKS fetch failure. When JWKS retrieval fails, istiod falls back to publicly known default keys, causing JWT verification to accept attacker-forged tokens. Direct exposure requires a RequestAuthentication resource configured with jwksUri and grants unauthorized access to resources protected by JWT authentication.

The record

CVE
CVE-2026-31837
Published
Mar 10, 2026
Updated
Mar 10, 2026
Vendor
Istio
Product
Istio
Classifications
CWE-200, T1606
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 10, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 10, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.27.8
  2. Affected versionversion=>= 1.28.0-alpha.0, < 1.28.5
  3. Affected versionversion=>= 1.29.0-alpha.0, < 1.29.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Istio · Istioversion=< 1.27.8; version=>= 1.28.0-alpha.0, < 1.28.5; version=>= 1.29.0-alpha.0, < 1.29.1

Published CVSS scores

8.7GitHub, Inc.CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
8.7IstioCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-200Exposure of Sensitive Information to an Unauthorized Actor
T1606Forge Web Credentials

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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