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
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
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-40894 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,333 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
OpenTelemetry.Api.NETOpenTelemetry.Extensions.PropagatorsReal-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
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | OpenTelemetry.Api | ≥ 0.5.0-beta.2&&< 1.15.3 | 1.15.3dotnet add package OpenTelemetry.Api --version 1.15.3 |
| .NETNuGet | OpenTelemetry.Extensions.Propagators | ≥ 1.3.1&&< 1.15.3 | 1.15.3dotnet add package OpenTelemetry.Extensions.Propagators --version 1.15.3 |
Detection & mitigation playbook
Open-source dependencyDetect
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
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-40894 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-40894. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-40894 in your dependencies?
O3 Security finds CVE-2026-40894 across NuGet dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.