How severe is CVE-2026-40891?

CVE-2026-40891 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over an adjacent network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2026-40891 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (9th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-40891?

CVE-2026-40891 affects Opentelemetry. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-40891?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-40891 have an EU (EUVD) identifier?

Yes. CVE-2026-40891 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-25268.

When was CVE-2026-40891 published?

CVE-2026-40891 was published on 2026-04-23 and last updated on 2026-06-17.

CVE-2026-40891

CVE-2026-40891 is a medium-severity vulnerability in Opentelemetry with a CVSS 3.x base score of 5.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-789.

Key facts

Severity: Medium (CVSS 3.x base score 5.3)
EPSS exploit prediction: 0% (9th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-25268
Weakness: CWE-789
Affected product: Opentelemetry
Published: 2026-04-23
Last modified: 2026-06-17

Description

OpenTelemetry dotnet is a dotnet telemetry framework. From 1.13.1 to before 1.15.2, When exporting telemetry over gRPC using the OpenTelemetry Protocol (OTLP), the exporter may parse a server-provided grpc-status-details-bin trailer during retry handling. Prior to the fix, a malformed trailer could encode an extremely large length-delimited protobuf field which was used directly for allocation, allowing excessive memory allocation and potential denial of service (DoS). This vulnerability is fixed in 1.15.2.

Frequently asked questions

What is CVE-2026-40891?: OpenTelemetry dotnet is a dotnet telemetry framework. From 1.13.1 to before 1.15.2, When exporting telemetry over gRPC using the OpenTelemetry Protocol (OTLP), the exporter may parse a server-provided grpc-status-details-bin trailer during retry handling. Prior to the fix, a malformed trailer could encode an extremely large length-delimited protobuf field which was used directly for allocation, allowing excessive memory allocation and potential denial of service (DoS). This vulnerability is fixed in 1.15.2.
How severe is CVE-2026-40891?: CVE-2026-40891 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over an adjacent network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2026-40891 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (9th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-40891?: CVE-2026-40891 affects Opentelemetry. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-40891?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-40891 have an EU (EUVD) identifier?: Yes. CVE-2026-40891 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-25268.
When was CVE-2026-40891 published?: CVE-2026-40891 was published on 2026-04-23 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:opentelemetry:opentelemetry:*:*:*:*:*:.net:*:*

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