CVE-2026-84303

MEDIUM

6.3

CVSS v4

Description

gRPC-Go is the Go language implementation of gRPC. Prior to 1.83.1, the xDS RBAC HTTP filter in internal/xds/httpfilter/rbac/rbac.go does not lowercase header matcher names in normalizeHeaderMatcher even though incoming metadata keys are lowercase. A DENY policy using a mixed-case name such as X-Role or User-Agent therefore does not match and fails open, allowing requests that should be rejected. The same case mismatch permits :Scheme or Grpc-Status to evade gRFC A41 validation and prevents Host from being rewritten to :authority. This issue is fixed in version 1.83.1.

CWE-178 CWE-863Incorrect Authorization

How to fix

Remediation Available

google.golang.org/grpcGo

Fixed in:1.83.1GO-2026-6441

Fixed in:1.83.1GHSA-qc2q-p7wx-3px3

TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v4 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

Impact

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Exploit Intelligence

0.31%probability of exploitation in 30 days

24thpercentile

Low risk: more likely to be exploited than 24% of all known CVEs.

References

Other references6

Related Vulnerabilities

Other CWE-178 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2025-27636	Medium	5.6	81%	-	Fix
CVE-2021-24347	High	8.8	54%	-	Fix
CVE-2020-12812	Critical	9.8	49%	KEV + Ransom	Fix
CVE-2003-0411	High	7.5	25%	-	-
CVE-2018-9845	Critical	9.8	13%	-	Fix
CVE-2001-0766	Critical	9.8	8.2%	-	-

Common questions

How do I fix CVE-2026-84303?

Upgrade google.golang.org/grpc to 1.83.1 or later.

Is CVE-2026-84303 being actively exploited?

Not that we know of. CVE-2026-84303 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.31% is the estimated probability that it will be exploited in the next 30 days. That is higher than 24% of all scored CVEs.

How severe is CVE-2026-84303?

CVE-2026-84303 has a CVSS v4 base score of 6.3, rated moderate. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

What does CVE-2026-84303 affect?

Published advisories record a fix for google.golang.org/grpc (Go). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-09-09.