Summary
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 Apollo Server v3 and v2 are no longer updated, as they have been EOL since 2024 and 2023 respectively.
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.
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.
A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use. Typical impact: denial of service when input is crafted to trigger backtracking.
CVE-2026-23897 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.13.0, 5.4.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
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.
Frequently Asked Questions
- What is CVE-2026-23897? CVE-2026-23897 is a high-severity inefficient regular expression (ReDoS) vulnerability in apollo-server (npm), affecting versions >= 2.0.0, <= 3.13.0. It is fixed in 4.13.0, 5.4.0. A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use.
- How severe is CVE-2026-23897? CVE-2026-23897 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which packages are affected by CVE-2026-23897?
apollo-server(npm) (versions >= 2.0.0, <= 3.13.0)@apollo/server(npm) (versions >= 4.2.0, < 4.13.0)
- Is there a fix for CVE-2026-23897? Yes. CVE-2026-23897 is fixed in 4.13.0, 5.4.0. Upgrade to this version or later.
- Is CVE-2026-23897 exploitable, and should I be worried? Whether CVE-2026-23897 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-23897 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-23897?
- Upgrade
@apollo/serverto 4.13.0 or later - Upgrade
@apollo/serverto 5.4.0 or later
- Upgrade