How severe is CVE-2026-40894?

CVE-2026-40894 has a CVSS score of 5.3/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2026-40894?

CVE-2026-40894 affects the following packages: OpenTelemetry.Api (NuGet), OpenTelemetry.Extensions.Propagators (NuGet). Ecosystems affected: NuGet.

How do I fix CVE-2026-40894?

Update OpenTelemetry.Api to 1.15.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-40894 is resolved across your whole dependency graph.

How do I detect CVE-2026-40894 in my NuGet dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for OpenTelemetry.Api, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-40894 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2026-40894 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-40894 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-40894?

CVE-2026-40894 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 40th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-40894?

CVE-2026-40894 is classified as CWE-789 (CWE-789). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-40894 published, and has it been updated?

CVE-2026-40894 was published on April 23, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

.NET

.NET NuGet

Not in CISA KEV

MEDIUM severity

CVE-2026-40894 — OpenTelemetry.Api

MEDIUMFix: open-telemetry/opentelemetry-dotnet#1048

CVE-2026-40894 is a medium-severity (CVSS 5.3) CWE-789 vulnerability in OpenTelemetry.Api. A fix is available for OpenTelemetry.Api — see the affected versions and patch details below.

OpenTelemetry dotnet: Excessive memory allocation when parsing OpenTelemetry propagation headers

Also known asGHSA-g94r-2vxg-569j

Published

Apr 23, 2026

Updated

Oct 28, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Nov 8, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-40894.

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs40th percentile — riskier than 40% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

2 pkgs affected

.NETOpenTelemetry.Api.NETOpenTelemetry.Extensions.Propagators

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.

Description

Summary

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.

Impact

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.

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.

Remediation

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

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
.NETNuGet	`OpenTelemetry.Api`	≥ 0.5.0-beta.2&&< 1.15.3	1.15.3`dotnet add package OpenTelemetry.Api --version 1.15.3`
.NETNuGet	`OpenTelemetry.Extensions.Propagators`	≥ 1.3.1&&< 1.15.3	1.15.3`dotnet add package OpenTelemetry.Extensions.Propagators --version 1.15.3`

Affected Products

3 products · 3 configurations

Application

opentelemetryopentelemetry

≥ 0.5.0 && < 1.15.3

range

Application

opentelemetry.apiopentelemetry

≥ 0.5.0 && < 1.15.3

range

Application

opentelemetry.extensions.propagatorsopentelemetry

> 1.3.0 && < 1.15.3

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for OpenTelemetry.Api, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update OpenTelemetry.Api to 1.15.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-40894 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Frequently Asked Questions

### Summary 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>()`](https://github.com/open-telemetry/opentelemetry-dotnet/blob/fc1a2864d1665bda857089e11fe9247e3c75637a/src/OpenTelemetry.Api/Context/Propagation/BaggagePropagator.cs#L93-L112) does not enforce the length limit of `8192` characters i