CVE-2026-41259: Mastodon is a free, open-source social network server based on ActivityPub. Prior to v4.5.9, v4.4.16, and v4.3.22, Mastodon allows restricting new user sign-up…

PriorityP342high7.5CVSS 3.1

AVNACLPRNUINSUCNIHAN

EPSS

0.21%

11.5th percentile

Mastodon is a free, open-source social network server based on ActivityPub. Prior to v4.5.9, v4.4.16, and v4.3.22, Mastodon allows restricting new user sign-up based on e-mail domain names, and performs basic validation on e-mail addresses, but fails to restrict characters that are interpreted differently by some mailing servers. This vulnerability is fixed in v4.5.9, v4.4.16, and v4.3.22.

Affected

6 ranges

Vendor	Product	Version range	Fixed in
joinmastodon	mastodon	< 4.3.22	4.3.22
joinmastodon	mastodon	>= 4.4.0 < 4.4.16	4.4.16
joinmastodon	mastodon	>= 4.5.0 < 4.5.9	4.5.9
mastodon	mastodon	< 4.3.22	4.3.22
mastodon	mastodon	—	—
mastodon	mastodon	—	—

CVSS provenance

nvdv3.17.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

nvdv4.08.2HIGHCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

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