How severe is CVE-2021-3761?

CVE-2021-3761 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-3761 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (65th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-3761?

CVE-2021-3761 primarily affects Cloudflare Octorpki. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-3761?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-3761 published?

CVE-2021-3761 was published on 2021-09-09 and last updated on 2026-06-17.

CVE-2021-3761

CVE-2021-3761 is a high-severity vulnerability in Cloudflare Octorpki with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-787.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 1% (65th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-787
Affected product: Cloudflare Octorpki
Published: 2021-09-09
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2021-3761?: 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.
How severe is CVE-2021-3761?: CVE-2021-3761 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-3761 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (65th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-3761?: CVE-2021-3761 primarily affects Cloudflare Octorpki. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-3761?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-3761 published?: CVE-2021-3761 was published on 2021-09-09 and last updated on 2026-06-17.

References

Affected products (2)

cpe:2.3:a:cloudflare:octorpki:*:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*

More vulnerabilities in Cloudflare Octorpki

CVE-2021-3978 — High (CVSS 7.5): When copying files with rsync, octorpki uses the "-a" flag 0, which forces rsync to copy binaries with the suid bit set…
CVE-2021-3907 — High (CVSS 7.4): OctoRPKI does not escape a URI with a filename containing "..", this allows a repository to create a file, (ex.…
CVE-2021-3908 — Medium (CVSS 5.9): OctoRPKI does not limit the depth of a certificate chain, allowing for a CA to create children in an ad-hoc fashion,…
CVE-2022-3616 — Medium (CVSS 5.4): Attackers can create long chains of CAs that would lead to OctoRPKI exceeding its max iterations parameter. In…
CVE-2021-3910 — Medium (CVSS 4.4): OctoRPKI crashes when encountering a repository that returns an invalid ROA (just an encoded NUL (\0) character).
CVE-2021-3909 — Medium (CVSS 4.4): OctoRPKI does not limit the length of a connection, allowing for a slowloris DOS attack to take place which makes…

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