Symfony: Ip Constraint public/private Modes Accept IPv4-Mapped and IPv4-Compatible IPv6 Addresses allowing SSRF Filter Bypass

Overview

The Symfony Validator component IpValidator incompletely classifies internal addresses in the filtered modes of the Ip constraint, so some internal addresses are accepted as public, which can lead to Server-Side Request Forgery (SSRF) in Symfony versions prior to 5.4.56, 6.x prior to 6.4.50, 7.x prior to 7.4.23, and 8.x prior to 8.1.11.

In these modes, IpValidator relies on the PHP flags FILTER_FLAG_NO_PRIV_RANGE and FILTER_FLAG_NO_RES_RANGE to classify addresses as public, private, or reserved. These flags do not cover shared address space (100.64.0.0/10) or IPv4-mapped, IPv4-compatible, and 6to4 IPv6 addresses, which can embed internal IPv4 addresses. A value such as ::ffff:127.0.0.1 can therefore pass validation even though it points to an internal host. Applications that rely on the Ip constraint to reject internal addresses, for example before making a server-side request to a user-supplied address, can be exposed to SSRF.

Affected

• symfony/validator < 5.4.56
• symfony/validator >= 6.0.0 < 6.4.50
• symfony/validator >= 7.0.0 < 7.4.23
• symfony/validator >= 8.0.0 < 8.1.11

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.