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CVE-2024-25623

Lack of media type verification of Activity Streams objects allows impersonation of remote accounts

8.5 HighFix available

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.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
Low
User interaction
None

What an attacker can affect

Confidentiality
Low
Integrity
High
Availability
None

Exploit likelihood

0.51%Up 0.5 points since Feb 20, 2024
90%50%10%1%

What each source reports

CVE List Score used 8.5

Lack of media type verification of Activity Streams objects allows impersonation of remote accounts

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.

Record
CVE-2024-25623
CVSS 3.1
8.5 HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:H/A:N
Weakness
CWE-434
Updated
2026-11-02
EUVDEUVD-2024-22944 8.5

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.

Record
EUVD-2024-22944
CVSS 3.1
8.5 HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:H/A:N
Updated
2026-11-03
NVD 8.5

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.

Record
CVE-2024-25623
CVSS 3.1
8.5 HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:H/A:N
CVSS 3.1
7.7 HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:N
Weakness
CWE-434
Updated
2026-11-02
OSV 8.5

Lack of media type verification of Activity Streams objects allows impersonation of remote accounts

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.

Record
CVE-2024-25623
CVSS 3.1
8.5 HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:H/A:N
Weakness
CWE-434
Updated
2026-11-02
OSVBIT-mastodon-2024-25623 No score

Lack of media type verification of Activity Streams objects allows impersonation of remote accounts

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.

Record
BIT-mastodon-2024-25623
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
mastodon
Bitnami
before 3.5.19, 4.0.0 up to 4.0.15, 4.1.0 up to 4.1.15, 4.2.0 up to 4.2.7
3.5.194.0.154.1.154.2.7

History

History
RecordedChangedSources
aliases, publishedEUVD
first indexedCVE List, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2024-25623 is a high vulnerability (CVSS 8.5) in Joinmastodon Mastodon, published February 19, 2024. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.51%, the 43rd percentile. Fixed in mastodon 3.5.19.

References

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