What is CVE-2024-25623?

CVE-2024-25623 is a high-severity vulnerability in Joinmastodon Mastodon, classified under Unrestricted Upload of File with Dangerous Type. CVSS score: 8.5/10. Published 2024-02-19.

How severe is CVE-2024-25623?

High severity. CVSS v3 base score is 8.5 out of 10.

Is CVE-2024-25623 known to be exploited?

2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Arbitrary file upload in Joinmastodon Mastodon

CVE-2024-25623

Mastodon is a free, open-source social network server based on ActivityPub. Prior to versions 4.2.7, 4.1.15, 4.0.15, and 3.5.19, when fetching remote statuses, Mastodon doesn't check that the response from the remote server has a `Content-Type` header value of the Activity Streams media type, which allows a threat actor to upload a crafted Activity Streams document to a remote server and make a Mastodon server fetch it, if the remote server accepts arbitrary user uploads. The vulnerability allows a threat actor to impersonate an account on a remote server that satisfies all of the following properties: allows the attacker to register an account; accepts arbitrary user-uploaded documents and places them on the same domain as the ActivityPub actors; and serves user-uploaded document in response to requests with an `Accept` header value of the Activity Streams media type. Versions 4.2.7, 4.1.15, 4.0.15, and 3.5.19 contain a fix for this issue.

Vulnerability class: Unrestricted File Upload

Published 2024-02-19 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 8.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:H/A:N.

EPSS exploit prediction

EPSS: 0.005 (42.3th percentile), scored 2026-10-20.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 42nd percentile — 42.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.005 · newest: 0.005 · change: -0.000

Affected products

Joinmastodon Mastodon
Mastodon — versions < 3.5.19, >= 4.0.0, < 4.0.15, >= 4.1.0, < 4.1.15

Weakness classification (CWE)

CWE-434 — Unrestricted Upload of File with Dangerous Type

Public proof-of-concept exploits

References

github.com/mastodon/mastodon/security/advisories/GHSA-jhrq-qvrm-qr36 (Vendor Advisory)
github.com/mastodon/mastodon/commit/9fee5e852669e26f970e278021302e1a203fc022 (Patch)

Frequently asked questions

What is CVE-2024-25623?: CVE-2024-25623 is a high-severity vulnerability in Joinmastodon Mastodon, classified under Unrestricted Upload of File with Dangerous Type. CVSS score: 8.5/10. Published 2024-02-19.
How severe is CVE-2024-25623?: High severity. CVSS v3 base score is 8.5 out of 10.
Is CVE-2024-25623 known to be exploited?: 2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.