CVE-2024-25623
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.
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
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 High
CVSS: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 High
CVSS: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 High
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:H/A:N - CVSS 3.1
- 7.7 High
CVSS: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 High
CVSS: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
| Package | Affected | Fixed |
|---|---|---|
mastodonBitnami |
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
| Recorded | Changed | Sources |
|---|---|---|
| aliases, published | EUVD | |
| first indexed | CVE 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.