Answer in brief
CVE-2026-72916 records a Medium severity (CVSS 6.3) vulnerability in Mastodon: SSRF Protection Bypass via IPv4-compatible IPv6 Addresses. The current sources do not mark it as known exploited. The current feed maps mastodon/mastodon (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 6.3. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps mastodon/mastodon (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| mastodon/mastodongeneric | < 4.4.21 || >= 4.5.0-beta.1, < 4.5.14 || >= 4.6.0-beta.1, < 4.6.4 | Not reported |
Published upstream
Aug 10, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Sep 9, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Aug 10, 2026
Mastodon is a free, open-source social network server based on ActivityPub. Prior to 4.4.21, 4.5.14, 4.6.4, and 4.7.0-beta.1, PrivateAddressCheck.private_address? in app/lib/private_address_check.rb normalized IPv4-mapped IPv6 addresses but did not recognize IPv4-compatible IPv6 addresses with IPAddr#ipv4_compat?. An attacker could supply an address in the omitted range to bypass the ALLOWED_PRIVATE_ADDRESSES protection and make Mastodon send HTTP requests to loopback interfaces, potentially accessing private resources and services. Exploitation requires a system that supports the obsolete IPv4-compatible IPv6 mechanism. This issue is fixed in versions 4.4.21, 4.5.14, 4.6.4, and 4.7.0-beta.1.
Quoted source text, attributed separately from HOL analysis.