How severe is CVE-2021-3909?

CVE-2021-3909 has a CVSS 3.x base score of 4.4, rated medium severity. It is exploitable over network with high attack complexity, requires high privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-3909 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (71st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-3909?

CVE-2021-3909 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-2021-3909?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-3909 published?

CVE-2021-3909 was published on 2021-11-11 and last updated on 2026-06-17.

CVE-2021-3909

CVE-2021-3909 is a medium-severity vulnerability in Cloudflare Octorpki with a CVSS 3.x base score of 4.4. 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-400.

Key facts

Severity: Medium (CVSS 3.x base score 4.4)
CVSS v2: 5.0
EPSS exploit prediction: 2% (71st percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-400
Affected product: Cloudflare Octorpki
Published: 2021-11-11
Last modified: 2026-06-17

Description

OctoRPKI does not limit the length of a connection, allowing for a slowloris DOS attack to take place which makes OctoRPKI wait forever. Specifically, the repository that OctoRPKI sends HTTP requests to will keep the connection open for a day before a response is returned, but does keep drip feeding new bytes to keep the connection alive.

Frequently asked questions

What is CVE-2021-3909?: OctoRPKI does not limit the length of a connection, allowing for a slowloris DOS attack to take place which makes OctoRPKI wait forever. Specifically, the repository that OctoRPKI sends HTTP requests to will keep the connection open for a day before a response is returned, but does keep drip feeding new bytes to keep the connection alive.
How severe is CVE-2021-3909?: CVE-2021-3909 has a CVSS 3.x base score of 4.4, rated medium severity. It is exploitable over network with high attack complexity, requires high privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-3909 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (71st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-3909?: CVE-2021-3909 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-2021-3909?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-3909 published?: CVE-2021-3909 was published on 2021-11-11 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-2021-3761 — High (CVSS 7.5): Any CA issuer in the RPKI can trick OctoRPKI prior to 1.3.0 into emitting an invalid VRP "MaxLength" value, causing RTR…
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).

All CVEs affecting Cloudflare Octorpki →

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