How severe is CVE-2026-31838?

CVE-2026-31838 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.

Is CVE-2026-31838 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (12th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-31838?

CVE-2026-31838 affects Istio. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-31838?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-31838 have an EU (EUVD) identifier?

Yes. CVE-2026-31838 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-10939.

When was CVE-2026-31838 published?

CVE-2026-31838 was published on 2026-03-10 and last updated on 2026-06-17.

CVE-2026-31838

CVE-2026-31838 is a medium-severity vulnerability in Istio with a CVSS 3.x base score of 5.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-863.

Key facts

Severity: Medium (CVSS 3.x base score 5.3)
CVSS v4: 6.9
EPSS exploit prediction: 0% (12th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-10939
Weakness: CWE-863
Affected product: Istio
Published: 2026-03-10
Last modified: 2026-06-17

Description

Istio is an open platform to connect, manage, and secure microservices. Prior to 1.29.1, 1.28.5, and 1.27.8, a vulnerability in Envoy RBAC header matching could allow authorization policy bypass when policies rely on HTTP headers that may contain multiple values. An attacker could craft requests with multiple header values in a way that causes Envoy to evaluate the header differently than intended, potentially bypassing authorization checks. This may allow unauthorized requests to reach protected services when policies depend on such header-based matching conditions. This vulnerability is fixed in 1.29.1, 1.28.5, and 1.27.8.

Frequently asked questions

What is CVE-2026-31838?: Istio is an open platform to connect, manage, and secure microservices. Prior to 1.29.1, 1.28.5, and 1.27.8, a vulnerability in Envoy RBAC header matching could allow authorization policy bypass when policies rely on HTTP headers that may contain multiple values. An attacker could craft requests with multiple header values in a way that causes Envoy to evaluate the header differently than intended, potentially bypassing authorization checks. This may allow unauthorized requests to reach protected services when policies depend on such header-based matching conditions. This vulnerability is fixed in 1.29.1, 1.28.5, and 1.27.8.
How severe is CVE-2026-31838?: CVE-2026-31838 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.
Is CVE-2026-31838 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (12th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-31838?: CVE-2026-31838 affects Istio. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-31838?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-31838 have an EU (EUVD) identifier?: Yes. CVE-2026-31838 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-10939.
When was CVE-2026-31838 published?: CVE-2026-31838 was published on 2026-03-10 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:istio:istio:*:*:*:*:*:*:*:*

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