How severe is CVE-2026-31866?

CVE-2026-31866 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-31866?

CVE-2026-31866 affects the following packages: github.com/open-feature/flagd/flagd (Go). Ecosystems affected: Go.

How do I fix CVE-2026-31866?

Update github.com/open-feature/flagd/flagd to 0.14.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-31866 is resolved across your whole dependency graph.

How do I detect CVE-2026-31866 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/open-feature/flagd/flagd, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-31866 if there is no patch (or I can't update yet)?

Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Is CVE-2026-31866 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-31866 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-31866?

CVE-2026-31866 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 41th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-31866?

CVE-2026-31866 is classified as CWE-770 (CWE-770). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-31866 published, and has it been updated?

CVE-2026-31866 was published on March 11, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹

🐹 Go

Not in CISA KEV

HIGH severity

CVE-2026-31866 — flagd

HIGHFix: open-feature/flagd@25c5fd7

CVE-2026-31866 is a high-severity (CVSS 7.5) CWE-770 vulnerability in github.com/open-feature/flagd/flagd. A fix is available for github.com/open-feature/flagd/flagd — see the affected versions and patch details below.

Allocation of Resources Without Limits or Throttling in flagd

Also known asGHSA-rmrf-g9r3-73pmGO-2026-4674

Published

Mar 11, 2026

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 7, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-31866.

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk+0.04%

Lower risk than most CVEs41th percentile — riskier than 41% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

🐹github.com/open-feature/flagd/flagd

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Details

flagd exposes OFREP (/ofrep/v1/evaluate/...) and gRPC (evaluation.v1, evaluation.v2) endpoints for feature flag evaluation. These endpoints are designed to be publicly accessible by client applications.

The evaluation context included in request payloads is read into memory without any size restriction. An attacker can send a single HTTP request with an arbitrarily large body, causing flagd to allocate a corresponding amount of memory. This leads to immediate memory exhaustion and process termination (e.g., OOMKill in Kubernetes environments).

flagd does not natively enforce authentication on its evaluation endpoints. While operators may deploy flagd behind an authenticating reverse proxy or similar infrastructure, the endpoints themselves impose no access control by default.

Impact

Denial of Service: A single crafted request can crash the flagd process.
Service Disruption: All applications relying on the affected flagd instance for feature flag evaluation will lose access to flag evaluations until the process restarts.
Repeated Exploitation: An attacker can continuously send oversized requests to prevent recovery.

Affected Endpoints

/ofrep/v1/evaluate/flags/{flagKey} (OFREP single flag evaluation)
/ofrep/v1/evaluate/flags (OFREP bulk evaluation)
flagd.evaluation.v1.Service/ResolveBoolean (gRPC/Connect)
flagd.evaluation.v1.Service/ResolveString (gRPC/Connect)
flagd.evaluation.v1.Service/ResolveFloat (gRPC/Connect)
flagd.evaluation.v1.Service/ResolveInt (gRPC/Connect)
flagd.evaluation.v1.Service/ResolveObject (gRPC/Connect)
flagd.evaluation.v1.Service/ResolveAll (gRPC/Connect)
flagd.evaluation.v2.Service/ResolveBoolean (gRPC/Connect)
flagd.evaluation.v2.Service/ResolveString (gRPC/Connect)
flagd.evaluation.v2.Service/ResolveFloat (gRPC/Connect)
flagd.evaluation.v2.Service/ResolveInt (gRPC/Connect)
flagd.evaluation.v2.Service/ResolveObject (gRPC/Connect)

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/open-feature/flagd/flagd`	all versions	0.14.2`go get github.com/open-feature/flagd/flagd@v0.14.2`

Affected Products

1 product · 1 configurations

Application

flagdopenfeature

< 0.14.2

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/open-feature/flagd/flagd, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/open-feature/flagd/flagd to 0.14.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-31866 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Frequently Asked Questions

## Details flagd exposes OFREP (`/ofrep/v1/evaluate/...`) and gRPC (`evaluation.v1`, `evaluation.v2`) endpoints for feature flag evaluation. These endpoints are designed to be publicly accessible by client applications. The evaluation context included in request payloads is read into memory without any size restriction. An attacker can send a single HTTP request with an arbitrarily large body, causing flagd to allocate a corresponding amount of memory. This leads to immediate memory exhaustion and process termination (e.g., OOMKill in Kubernetes environments). flagd does not natively enforc

O3 Security · Impact-Aware SCA

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CVSS Score

7.5/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Raw vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CWE Classification

CWE-770CWE-770

Weaponization

No Nuclei template, Metasploit module or public proof-of-concept found.

Timeline

Disclosed

Mar 11, 2026

Last updated

Oct 28, 2026

Identifiers

CVE-2026-31866

GHSA-rmrf-g9r3-73pm

GO-2026-4674

References

Advisorygithub.com · CVE 2026 31866.json Advisorygithub.com · GHSA rmrf g9r3 73pm Advisorynvd.nist.gov · CVE 2026 31866 Fixgithub.com · 25c5fd7e80c26eb2c00b20317b2456fe6f927ea3 Packagegithub.com · flagd

Related vulnerabilities

Also affects flagd

This CVE is high severity, in line with the other 1 CVE affecting flagd.

GHSA-4c5f-9mj4-m247

Same weakness: CWE-770

This CVE is high severity; 3 of 7 other CVEs with CWE-770 are rated as high or higher (top: high).

CVE-2026-116773CVE-2026-119208CVE-2026-116775CVE-2026-116696CVE-2026-119209GHSA-vpp8-g58w-m8mpGHSA-2hw4-c9m4-f2fjBrowse all CWE-770

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedOct 28, 2026

CVE-2026-31866 — flagd

Exploitation Status

No confirmed exploitation observed yet

EPSS Exploitation Probability

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

Description

Details

Impact

Affected Endpoints

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Frequently Asked Questions

Is CVE-2026-31866 in your dependencies?