VulnerabilityDeferred

CVE-2026-72916

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.

MEDIUM 6.3EPSS 0.36%

Does this matter?

Lower severity and a low EPSS score (0.36%). Track it; it rarely justifies an emergency change on its own.

Description

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.

CVSS 4.0: 6.3 MEDIUMCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:L/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M
EPSS: 0.36% probability · 29th percentile
CISA KEV: Not listed
Weakness: CWE-918, CWE-1286
Source: security-advisories@github.com

References

Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.