Symfony 6.3.8 has just been released.
Here is the list of the most important changes since 6.3.7:

bug #51666 [RateLimiter] CompoundLimiter was accepting requests even when some limiters already consumed all tokens (@10n)
security #cve-2023-46734 [TwigBridge] Ensure CodeExtension’s filters properly escape their input (@nicolas-grekas, @GromNaN)
security #cve-2023-46735 [Webhook] Remove user-submitted type from HTTP response (@nicolas-grekas)
security #cve-2023-46733 [Security] Fix possible session fixation when only the token changes (@RobertMe)
bug #52514 [FrameworkBundle] Don’t reference SYMFONY_IDE env var in non-debug mode (@nicolas-grekas)
bug #52506 [SecurityBundle] wire the secret for Symfony 6.4 compatibility (@xabbuh)
bug #52496 [VarDumper] Accept mixed key on DsPairStub (@marc-mabe)
bug #52502 [Config] Prefixing FileExistenceResource::__toString() to avoid conflict with FileResource (@weaverryan)
bug #52491 [String] Method toByteString conversion using iconv is unreachable (@Vincentv92)
bug #52488 [HttpKernel] Fix PHP deprecation (@nicolas-grekas)
bug #52476 [Messenger] fix compatibility with Doctrine DBAL 4 (@xabbuh)
bug #52474 [HttpFoundation] ensure string type with mbstring func overloading enabled (@xabbuh)
bug #52472 [HttpClient][WebProfilerBundle] Do not generate cURL command when files are uploaded (@MatTheCat)
bug #52457 [Cache][HttpFoundation][Lock] Fix empty username/password for PDO PostgreSQL (@HypeMC)
bug #52443 [Yaml] Fix uid binary parsing (@mRoca)
bug #52429 [HttpClient] Replace escapeshellarg to prevent overpassing ARG_MAX (@alexandre-daubois)
bug #52442 Disable the „Copy as cURL“ button when the debug info are disabled (@stof)
bug #52444 Remove full DSNs from exception messages (@nicolas-grekas)
bug #52428 [HttpKernel] Preventing error 500 when function putenv is disabled (@ShaiMagal)
bug #52408 [Yaml] Fix block scalar array parsing (@NickSdot)
bug #52132 [Console] Fix horizontal table top border is incorrectly rendered (@OskarStark)
bug #52367 [Uid] Fix UuidV7 collisions within the same ms (@nicolas-grekas)
bug #52222 [MonologBridge] Fix support for monolog 3.0 (@louismariegaborit)

Want to upgrade to this new release? Because Symfony protects
backwards-compatibility very closely, this should be quite easy. Use
SymfonyInsight upgrade reports
to detect the code you will need to change in your project and
read our upgrade
documentation to learn more.

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