CVE-2026-40894

The implementation details of the baggage, B3 and Jaeger processing code in the OpenTelemetry.Api and OpenTelemetry.Extensions.Propagators NuGet packages can allocate excessive memory when parsing which could create a potential denial of service (DoS) in the consuming application.

Details

Exceeding Limits

BaggagePropagator.Inject<T>() does not enforce the length limit of 8192 characters if the injected baggage contains only one item.

This change was introduced by #1048.

Excessive allocation

The following methods eagerly allocate intermediate arrays before applying size limits.

• BaggagePropagator.Extract<T>() - this change was introduced by #1048.
• BaggagePropagator.Inject<T>() - this change was introduced by #1048.
• B3Propagator.Extract<T>() - this change was introduced by #533.
• B3Propagator.Extract<T>() - this change was introduced by #3244.
• JaegerPropagator.Extract<T>() - this change was introduced by #3309.

Mitigation

HTTP servers often set maximum limits on the length of HTTP request headers, such as Internet Information Services (IIS) which sets a default limit of 16KB and nginx which sets a default limit of 8KB.

Workarounds

Possible workarounds include:

• Configuring appropriate HTTP request header limits.
• Disabling baggage and/or trace propagation.

Excessively large propagation headers, particularly in degenerate/malformed cases that consist or large numbers of delimiter characters, can allocate excessive amounts of memory for intermediate storage of parsed content relative to the size of the original input.

CVE-2026-40894 has a CVSS score of 5.3 (Medium). 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 (1.15.3); upgrading removes the vulnerable code path.

Kodem intelligence

#7061 refactors the handling of baggage, B3 and Jaeger propagation headers to stop parsing eagerly when limits are exceeded and avoid allocating intermediate arrays.

1. What is CVE-2026-40894? CVE-2026-40894 is a medium-severity security vulnerability in OpenTelemetry.Api (nuget), affecting versions >= 0.5.0-beta.2, < 1.15.3. It is fixed in 1.15.3.
2. How severe is CVE-2026-40894? CVE-2026-40894 has a CVSS score of 5.3 (Medium). 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.
3. Which packages are affected by CVE-2026-40894?
   • OpenTelemetry.Api (nuget) (versions >= 0.5.0-beta.2, < 1.15.3)
   • OpenTelemetry.Extensions.Propagators (nuget) (versions >= 1.3.1, < 1.15.3)
4. Is there a fix for CVE-2026-40894? Yes. CVE-2026-40894 is fixed in 1.15.3. Upgrade to this version or later.
5. Is CVE-2026-40894 exploitable, and should I be worried? Whether CVE-2026-40894 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
6. What actually determines whether CVE-2026-40894 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.
7. How do I fix CVE-2026-40894?
   • Upgrade OpenTelemetry.Api to 1.15.3 or later
   • Upgrade OpenTelemetry.Extensions.Propagators to 1.15.3 or later