medium4.3
CVE-2026-2455
Mattermost fails to canonicalize IPv4-mapped IPv6 addresses before reserved IP validation
Impact
Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to canonicalize IPv4-mapped IPv6 addresses before reserved IP validation which allows an attacker to perform SSRF attacks against internal services via IPv4-mapped IPv6 literals (e.g., [::ffff:127.0.0.1]).. Mattermost Advisory ID: MMSA-2026-00585
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| go | github.com/mattermost/mattermost/server/v8 | < 8.0.0-20260129133647-5d787969c2d5 | 8.0.0-20260129133647-5d787969c2d5 |
| go | github.com/mattermost/mattermost-server | < 5.3.2-0.20260129133647-5d787969c2d5 | 5.3.2-0.20260129133647-5d787969c2d5 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Mattermost | Mattermost Server | from 10.11.0 before 10.11.11 from 11.2.0 before 11.2.3 from 11.3.0 before 11.3.1 |