CVE-2026-23897

Impact

The default configuration of startStandaloneServer from @apollo/server/standalone is vulnerable to Denial of Service (DoS) attacks through specially crafted request bodies with exotic character set encodings.

This issue does not affect users that use @apollo/server as a dependency for integration packages, like @as integrations/express5 or @as-integrations/next, only direct usage of startStandaloneServer.

Who is impacted

Users directly using startStandaloneServer from @apollo/server/standalone.

This issue affects Apollo Server from v5.0.0 through v5.3.x.

It also affects all releases of the end-of-life major versions v4, v3, and v2.  Although Apollo Server v4 is EOL and Apollo no longer commits to providing support or updates for it, a fix for it was released in v4.13.0.  Apollo Server v3 and v2 are no longer updated, as they have been EOL since 2024 and 2023 respectively.

Patches

Patches for this issue are released as @apollo/server versions 5.4.0 and 4.13.0.

In accordance with RFC 7159, these versions now only accept request bodies encoded in UTF-8, UTF-16 (LE or BE), or UTF-32 (LE or BE). Any other character set will be rejected with a 415 Unsupported Media Type error. Note that the more recent JSON RFC, [RFC 8259 (https://datatracker.ietf.org/doc/html/rfc8259#section-8.1), is more strict and will only allow UTF-8. Since this is a minor release, we have chosen to remain compatible with the more permissive RFC 7159 for now. In a future major release, the restriction may be tightened further to only allow UTF-8.

Workarounds

Users of apollo-server v2 or v3 that cannot upgrade for some reason could switch from the standalone apollo-server

package to an integration package like apollo-server-express or apollo-server-koa and set up their own server. Please note that these old packages are generally EOL and do not receive any more support or bug fixes. This can only be seen as a short-term workaround. Updating to @apollo/server v5 should be a priority.