How severe is CVE-2021-3761?

CVE-2021-3761 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-3761?

CVE-2021-3761 affects the following packages: github.com/cloudflare/cfrpki (Go). Ecosystems affected: Go.

How do I fix CVE-2021-3761?

Update github.com/cloudflare/cfrpki to 1.3.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-3761 is resolved across your whole dependency graph.

How do I detect CVE-2021-3761 in my Go dependencies?

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

How do I mitigate CVE-2021-3761 if there is no patch (or I can't update yet)?

Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable.

Is CVE-2021-3761 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-3761 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-2021-3761?

CVE-2021-3761 has an EPSS (Exploit Prediction Scoring System) score of 1.2%, placing it in the 68th 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-2021-3761?

CVE-2021-3761 is classified as Out-of-bounds Write (CWE-787). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-3761 published, and has it been updated?

CVE-2021-3761 was published on September 9, 2021 and was last updated on July 8, 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-2021-3761 — cfrpki

HIGHFix: cloudflare/cfrpki#90

CVE-2021-3761 is a high-severity (CVSS 7.5) Out-of-bounds Write vulnerability in github.com/cloudflare/cfrpki. A fix is available for github.com/cloudflare/cfrpki — see the affected versions and patch details below.

OctoRPKI lacks contextual out-of-bounds check when validating RPKI ROA maxLength values

Also known asGHSA-c8xp-8mf3-62h9GO-2022-0246

Published

Sep 9, 2021

Updated

Jul 8, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

1.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs68th percentile — riskier than 68% of all scored CVEsHighest risk

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

How urgent is this, really

CVE-2021-3761 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,987 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

🐹github.com/cloudflare/cfrpki

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

Impact

An attacker can use this to disable RPKI Origin Validation in a victim network (for example AS 13335 - Cloudflare) prior to launching a BGP hijack which during normal operations would be rejected as "RPKI invalid". Additionally, in certain deployments RTR session flapping in and of itself also could cause BGP routing churn, causing availability issues.

Patches

https://github.com/cloudflare/cfrpki/commit/a8db4e009ef217484598ba1fd1c595b54e0f6422

https://github.com/cloudflare/cfrpki/releases/tag/v1.3.0

For more information

If you have any questions or comments about this advisory:

Email us at [email protected]

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/cloudflare/cfrpki`	all versions	1.3.0`go get github.com/cloudflare/cfrpki@v1.3.0`

Affected Products

2 products · 2 configurations

Application

octorpkicloudflare

< 1.3.0

range

debian linuxdebian

1 version

11.0

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/cloudflare/cfrpki, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/cloudflare/cfrpki to 1.3.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-3761 is resolved across your whole dependency graph.
Workarounds
Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable.

Frequently Asked Questions

Any CA issuer in the RPKI can trick OctoRPKI prior to https://github.com/cloudflare/cfrpki/commit/a8db4e009ef217484598ba1fd1c595b54e0f6422 into emitting an invalid VRP "MaxLength" value, causing RTR sessions to terminate. ### Impact An attacker can use this to disable RPKI Origin Validation in a victim network (for example AS 13335 - Cloudflare) prior to launching a BGP hijack which during normal operations would be rejected as "RPKI invalid". Additionally, in certain deployments RTR session flapping in and of itself also could cause BGP routing churn, causing availability issues. ### Patc

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-787Out-of-bounds Write

Weaponization

No known public exploit tooling found.

OpenSSF Scorecard

Package health score

cfrpki

4.7/10

Code-Review7/10

Maintained0/10

Branch-ProtectionN/A

Assessed Oct 5, 2026

Timeline

Disclosed

Sep 9, 2021

Last updated

Jul 8, 2026

Identifiers

CVE-2021-3761

GHSA-c8xp-8mf3-62h9

GO-2022-0246

References

Advisorydebian.org Advisorynvd.nist.gov Fixgithub.com Webgithub.com Webgithub.com Webgithub.com Webpkg.go.dev Packagegithub.com/cloudflare/cfrpki

Related vulnerabilities

This CVE is high severity; 4 of 8 other CVEs affecting cfrpki are rated as high or higher (top: high).

CVE-2022-3616GHSA-3jhm-87m6-x959GHSA-8459-6rc9-8vf8CVE-2021-3978CVE-2021-3910CVE-2021-3909CVE-2021-3907CVE-2021-3908

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedJul 8, 2026

CVE-2021-3761 — cfrpki

EPSS Exploitation Probability

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

Description

Impact

Patches

For more information

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Frequently Asked Questions

Is CVE-2021-3761 in your dependencies?