CVE-2026-50128
Mastodon is a free, open-source social network server based on ActivityPub.
- Severity
- 5.3 / 10
- Medium · CVSS 3.1
- Exploit chance (EPSS)
- 0.18%
- Chance of exploitation in the next 30 days. Higher than 7.90% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-354 Improper Validation of Integrity Check Value
- Fix
- None yet
- No fixed version published
Description
Mastodon is a free, open-source social network server based on ActivityPub. From 4.3.0 until 4.5.11 and 4.4.18, Mastodon has a feature to let websites credit authors of their articles. To prevent false attribution claims, Mastodon uses the attributionDomains JSON-LD term, however, an error in how it is defined makes Linked Data Signatures on the toot:attributionDomains property ineffective. An attacker can arbitrarily modify the attributionDomains value of a legitimately signed Update activity and bypass Mastodon’s signature verification. This vulnerability is fixed in 4.5.11 and 4.4.18.
How to fix
No fixed version has been published yet. Until one is, remove or replace the package, or turn off or isolate the affected feature. This page updates when a fix ships.
Severity breakdown
CVSS 3.1 5.3
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- Low
- Availability
- None
Weakness
CWE-354: Improper Validation of Integrity Check Value
The product does not validate or incorrectly validates the integrity check values or "checksums" of a message. This may prevent it from detecting if the data has been modified or corrupted in transmission.
How to prevent it
- Implementation: Ensure that the checksums present in messages are properly checked in accordance with the protocol specification before they are parsed and used.
References
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-5cwg-6vw7-rj6p Forge: AES-GCM authentication bypass via unvalidated tagLength option | Medium | Same weakness, CWE-354 |
| GHSA-jc66-7q78-782g Forge: PKCS#12 MAC forgery and constant-key PBE via zero iteration count | High | Same weakness, CWE-354 |
| EEF-CVE-2026-65625 Attacker-controlled AES-GCM authentication tag length allows tag forgery in jose | Not rated yet | Same weakness, CWE-354 |
| GHSA-8hxf-qr8p-62x4 zip: AES Entry HMAC Authentication Bypass on Premature EOF | Medium | Same weakness, CWE-354 |
| GHSA-q6j5-fjx5-2mc3 pnpm Has an Integrity Check Bypass via Missing Lockfile Integrity Field | High | Same weakness, CWE-354 |
| GHSA-pvmv-cwg8-v6c8 Zebra v4.4.0 still accepts V5 SIGHASH_SINGLE without a corresponding output | High | Same weakness, CWE-354 |
| GHSA-cwfq-rfcr-8hmp Zebra's Transparent SIGHASH_SINGLE Handling Diverges from zcashd for Corresponding Outputs | High | Same weakness, CWE-354 |
| GHSA-fhh2-gg7w-gwpq nginx-ui Backup Restore Allows Tampering with Encrypted Backups | Critical | Same weakness, CWE-354 |
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