CVE-2023-46733: Symfony possible session fixation vulnerability

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.7% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2023-11-10 · updated 2026-06-17
Weakness: CWE-384

Description

Symfony is a PHP framework for web and console applications and a set of reusable PHP components. Starting in versions 5.4.21 and 6.2.7 and prior to versions 5.4.31 and 6.3.8, `SessionStrategyListener` does not migrate the session after every successful login. It does so only in case the logged in user changes by means of checking the user identifier. In some use cases, the user identifier doesn't change between the verification phase and the successful login, while the token itself changes from one type (partially-authenticated) to another (fully-authenticated). When this happens, the session id should be regenerated to prevent possible session fixations, which is not the case at the moment. As of versions 5.4.31 and 6.3.8, Symfony now checks the type of the token in addition to the user identifier before deciding whether the session id should be regenerated.

Affected products

symfony: from 5.4.21 before 5.4.31; from 6.2.7 before 6.3.8 — fixed in 5.4.31, 6.3.8

How to fix

Upgrade to a fixed version: symfony 5.4.31, 6.3.8. Check the vendor advisory for mitigations.

References

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