CVE-2021-3761

Name: CVE-2021-3761
Creator: NVD / NIST
Published: 2021-09-09T14:15:09.397+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.5/10EPSS 1.18%

Last modified Jun 17, 2026

CVE-2021-3761 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. Any CA issuer in the RPKI can trick OctoRPKI prior to 1.3.0 into emitting an invalid VRP "MaxLength" value, causing RTR sessions to terminate. 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". EPSS estimates a 1.18% chance of exploitation in the next 30 days.

Description

Any CA issuer in the RPKI can trick OctoRPKI prior to 1.3.0 into emitting an invalid VRP "MaxLength" value, causing RTR sessions to terminate. 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.

Metrics

CVSS 3.1

7.5/10

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

EPSS Probability

1.18%

63.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-787

Affected Software

Vendor	Product	Versions
Cloudflare	Octorpki	< 1.3.0
Debian	Debian Linux	11.0

References

https://github.com/cloudflare/cfrpki/security/advisories/GHSA-c8xp-8mf3-62h9Patch, Third Party Advisory
https://www.debian.org/security/2022/dsa-5041Third Party Advisory
https://github.com/cloudflare/cfrpki/security/advisories/GHSA-c8xp-8mf3-62h9Patch, Third Party Advisory
https://www.debian.org/security/2022/dsa-5041Third Party Advisory

Timeline

Published: Sep 9, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-3761?

How severe is CVE-2021-3761?

CVE-2021-3761 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 1.18% probability of exploitation in the next 30 days.

How do I fix CVE-2021-3761?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-3761?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST