CVE-2026-46629: Twig: Unbounded formatter memoisation in twig/intl-extra keyed on template-controlled arguments
Description
IntlExtension memoises every \IntlDateFormatter and \NumberFormatter it creates in instance-level arrays keyed on a hash that includes locale, pattern, attrs and other values that are ordinary named arguments of the formatdatetime / formatdate / formattime / formatnumber / formatcurrency filters. There is no size limit and no eviction.
A template that iterates over many distinct pattern (or locale, or groupingused, ...) values therefore allocates one ICU formatter object per distinct value and pins it for the entire lifetime of the Twig\Environment. Because ICU allocates its backing buffers outside the Zend memory manager, this growth is not bounded by memorylimit. On long-running runtimes (RoadRunner, Swoole, FrankenPHP worker mode, ReactPHP) where the Environment outlives a single request, the cache also accumulates across requests.
Resolution
The formatter caches are now bounded in size (100 entries each) and evict on a FIFO basis.
Credits
Twig would like to thank Claude Mythos Preview (via Project Glasswing) for reporting the issue and providing the fix.
Other sources
Twig is a template language for PHP. Prior to 3.26.0, twig/intl-extra memoises IntlDateFormatter and NumberFormatter instances in arrays keyed by template-controlled filter arguments such as locale, pattern, and attrs, allowing a template to allocate many ICU formatter objects that remain pinned for the lifetime of the Twig\Environment. This issue is fixed in version 3.26.0.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
composer/twig/intl-extrato a version that resolves this vulnerability.Fixed in 3.26.0 - Upgrade
Upgrade
twig/intl-extrato a version that resolves this vulnerability.Fixed in 3.26.0 - Compensating control
On long-running PHP runtimes where a single Twig\Environment outlives requests (e.g., RoadRunner, Swoole, FrankenPHP worker mode, ReactPHP), avoid templates that vary template-controlled formatter arguments (such as locale, pattern, and attrs for format_datetime/format_date/format_time/format_number/format_currency filters) across requests until upgrading to twig/intl-extra 3.26.0.
Event History
Frequently Asked Questions
What is the severity of CVE-2026-46629?
CVE-2026-46629 has a medium severity rating of 5.3 on the CVSS scale.
How do I fix CVE-2026-46629?
To remediate CVE-2026-46629, update the affected composer/twig/intl-extra package to the latest version that addresses this vulnerability.
What are the risks associated with CVE-2026-46629?
CVE-2026-46629 poses the risk of unbounded formatter memoization leading to potential denial of service in applications using Twig.
Which software is affected by CVE-2026-46629?
The vulnerability CVE-2026-46629 affects the composer/twig/intl-extra and Symfony Twig packages.
When was CVE-2026-46629 published?
CVE-2026-46629 was published on May 21, 2026.