CVE-2026-42348 — OpenTelemetry.OpAmp.Client
MEDIUMFix: open-telemetry/opentelemetry-dotnet-contrib#4116CVE-2026-42348 is a medium-severity (CVSS 5.9) CWE-789 vulnerability in OpenTelemetry.OpAmp.Client. A fix is available for OpenTelemetry.OpAmp.Client — see the affected versions and patch details below.
OpAMP client reads unbounded HTTP response bodies
Exploitation Status
No confirmed exploitation observed yet
- 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-2026-42348.
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-2026-42348 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 377,636 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.OpAmp.ClientReal-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
When receiving responses from the OpAMP server over HTTP, the OpAMP client allocates an unbounded buffer to read all bytes from the server, with no upper-bound on the number of bytes consumed.
This could cause memory exhaustion in the consuming application if the configured OpAMP server is attacker-controlled (or a network attacker can MitM the connection) and an extremely large body is returned in the response.
Details
#2926 introduced the initial HTTP transport components which uses ReadAsByteArrayAsync to copy the HttpResponseMessage.Content into a byte array. This code path allows an unbounded read of the entire HTTP response message.
Impact
If an application using the OpAMP client is configured to use an OpAMP server that is attacker-controlled (or a network attacker can MitM the connection) and an extremely large body is returned in the response, the application could have its memory exhausted and create a denial-of-service condition.
Mitigation
The application's configured OpAMP server needs to behave maliciously. If the OpAMP server is a well-behaved implementation, response bodies should not be excessively large.
Workarounds
None known.
Remediation
#4116 updates the OpAMP client HTTP transport to limit the maximum size of responses to 128KB.
Resources
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | OpenTelemetry.OpAmp.Client | all versions | 0.2.0-alpha.1dotnet add package OpenTelemetry.OpAmp.Client --version 0.2.0-alpha.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for OpenTelemetry.OpAmp.Client, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update OpenTelemetry.OpAmp.Client to 0.2.0-alpha.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-42348 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-2026-42348 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-42348. 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-2026-42348 in your dependencies?
O3 Security finds CVE-2026-42348 across NuGet dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.