How severe is CVE-2026-33869?

CVE-2026-33869 has a CVSS 3.x base score of 4.8, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability low.

Is CVE-2026-33869 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (6th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-33869?

CVE-2026-33869 affects Joinmastodon Mastodon. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-33869?

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

Does CVE-2026-33869 have an EU (EUVD) identifier?

Yes. CVE-2026-33869 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-16785.

When was CVE-2026-33869 published?

CVE-2026-33869 was published on 2026-03-27 and last updated on 2026-06-17.

CVE-2026-33869

CVE-2026-33869 is a medium-severity vulnerability in Joinmastodon Mastodon with a CVSS 3.x base score of 4.8. 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-863.

Key facts

Severity: Medium (CVSS 3.x base score 4.8)
EPSS exploit prediction: 0% (6th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-16785
Weakness: CWE-863
Affected product: Joinmastodon Mastodon
Published: 2026-03-27
Last modified: 2026-06-17

Description

Mastodon is a free, open-source social network server based on ActivityPub. In versions on the 4.5.x branch prior to 4.5.8 and on the 4.4.x branch prior to 4.4.15, an attacker that knows of a quote before it has reached a server can prevent it from being correctly processed on that server. The vulnerability has been patched in Mastodon 4.5.8 and 4.4.15. Mastodon 4.3 and earlier are not affected because they do not support quotes.

Frequently asked questions

What is CVE-2026-33869?: Mastodon is a free, open-source social network server based on ActivityPub. In versions on the 4.5.x branch prior to 4.5.8 and on the 4.4.x branch prior to 4.4.15, an attacker that knows of a quote before it has reached a server can prevent it from being correctly processed on that server. The vulnerability has been patched in Mastodon 4.5.8 and 4.4.15. Mastodon 4.3 and earlier are not affected because they do not support quotes.
How severe is CVE-2026-33869?: CVE-2026-33869 has a CVSS 3.x base score of 4.8, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability low.
Is CVE-2026-33869 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (6th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-33869?: CVE-2026-33869 affects Joinmastodon Mastodon. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-33869?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-33869 have an EU (EUVD) identifier?: Yes. CVE-2026-33869 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-16785.
When was CVE-2026-33869 published?: CVE-2026-33869 was published on 2026-03-27 and last updated on 2026-06-17.

References

https://github.com/mastodon/mastodon/security/advisories/GHSA-q4g8-82c5-9h33

Affected products (1)

cpe:2.3:a:joinmastodon:mastodon:*:*:*:*:*:*:*:*

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