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GHSA-4j38-f5cw-54h7
No affected components available
Description
The spaceless filter is registered with is_safe => ['html'], which means Twig's autoescaper does not escape its output in an HTML context. As a result, applying spaceless to attacker-controlled input that contains markup emits the markup unescaped even when the developer never wrote |raw and autoescape is enabled.
Example:
{% set payload = '<script>alert()</script>' %}
{{ payload }} {# escaped #}
{{ payload|spaceless }} {# not escaped #}
The filter is deprecated but still functional. With the deprecation, some downstream projects (e.g. Drupal modules) have duplicated the filter and inherited the same is_safe flag.
Resolution
The spaceless filter no longer marks its output as safe. Documentation has been updated to warn that spaceless should not be applied to unsanitised user input.
Credits
Twig would like to thank Pierre Rudloff for reporting the issue.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights.
Limited exploitation activity has been observed. Close monitoring and planned remediation are recommended.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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