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
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
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-31866 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
github.com/open-feature/flagd/flagdReal-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
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/open-feature/flagd/flagd | all versions | 0.14.2go get github.com/open-feature/flagd/flagd@v0.14.2 |
Detection & mitigation playbook
Open-source dependencyDetect
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
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-31866 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-31866. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-31866 in your dependencies?
O3 Security finds CVE-2026-31866 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.