{"id":"CVE-2026-40894","aliases":["GHSA-g94r-2vxg-569j"],"url":"https://o3.security/vulnerability/CVE-2026-40894","summary":"OpenTelemetry dotnet: Excessive memory allocation when parsing OpenTelemetry propagation headers","details":"### Summary\n\nThe 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.\n\n### Details\n\n#### Exceeding Limits\n\n[`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 if the injected baggage contains only one item.\n\nThis change was introduced by #1048.\n\n#### Excessive allocation\n\nThe following methods eagerly allocate intermediate arrays before applying size limits.\n\n- [`BaggagePropagator.Extract<T>()`](https://github.com/open-telemetry/opentelemetry-dotnet/blob/888d1bf2489fb7408d3c5e8758a5bbffa89a8fb2/src/OpenTelemetry.Api/Context/Propagation/BaggagePropagator.cs#L52-L55) - this change was introduced by #1048.\n- [`BaggagePropagator.Inject<T>()`](https://github.com/open-telemetry/opentelemetry-dotnet/blob/888d1bf2489fb7408d3c5e8758a5bbffa89a8fb2/src/OpenTelemetry.Api/Context/Propagation/BaggagePropagator.cs#L138-L157) - this change was introduced by #1048.\n- [`B3Propagator.Extract<T>()`](https://github.com/open-telemetry/opentelemetry-dotnet/blob/888d1bf2489fb7408d3c5e8758a5bbffa89a8fb2/src/OpenTelemetry.Extensions.Propagators/B3Propagator.cs#L203-L207) - this change was introduced by #533.\n- [`B3Propagator.Extract<T>()`](https://github.com/open-telemetry/opentelemetry-dotnet/blob/888d1bf2489fb7408d3c5e8758a5bbffa89a8fb2/src/OpenTelemetry.Api/Context/Propagation/B3Propagator.cs#L204-L214) - this change was introduced by #3244.\n- [`JaegerPropagator.Extract<T>()`](https://github.com/open-telemetry/opentelemetry-dotnet/blob/888d1bf2489fb7408d3c5e8758a5bbffa89a8fb2/src/OpenTelemetry.Extensions.Propagators/JaegerPropagator.cs#L150-L154) - this change was introduced by #3309.\n\n### Impact\n\nExcessively 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.\n\n### Mitigation\n\nHTTP servers often set maximum limits on the length of HTTP request headers, such as [Internet Information Services (IIS)](https://learn.microsoft.com/iis/configuration/system.webserver/security/requestfiltering/requestlimits/headerlimits/) which sets a default limit of 16KB and [nginx](https://nginx.org/docs/http/ngx_http_core_module.html#large_client_header_buffers) which sets a default limit of 8KB.\n\n### Workarounds\n\nPossible workarounds include:\n\n- Configuring appropriate HTTP request header limits.\n- Disabling baggage and/or trace propagation.\n\n### Remediation\n\n[#7061](https://github.com/open-telemetry/opentelemetry-dotnet/pull/7061) refactors the handling of baggage, B3 and Jaeger propagation headers to stop parsing eagerly when limits are exceeded and avoid allocating intermediate arrays.","published":"2026-04-23T18:03:28.211Z","modified":"2026-08-29T11:31:04.000089971Z","cvss":{"score":5.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"},"epss":{"score":0.00458,"percentile":0.37784,"asOf":"2026-08-14"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"NuGet","name":"OpenTelemetry.Api","fixedVersion":"1.15.3"},{"ecosystem":"NuGet","name":"OpenTelemetry.Extensions.Propagators","fixedVersion":"1.15.3"}],"fix":{"url":"https://github.com/open-telemetry/opentelemetry-dotnet/pull/1048","label":"open-telemetry/opentelemetry-dotnet#1048"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/40xxx/CVE-2026-40894.json"},{"type":"ADVISORY","url":"https://github.com/open-telemetry/opentelemetry-dotnet/security/advisories/GHSA-g94r-2vxg-569j"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-40894"},{"type":"FIX","url":"https://github.com/open-telemetry/opentelemetry-dotnet/pull/1048"},{"type":"FIX","url":"https://github.com/open-telemetry/opentelemetry-dotnet/pull/3244"},{"type":"FIX","url":"https://github.com/open-telemetry/opentelemetry-dotnet/pull/3309"},{"type":"FIX","url":"https://github.com/open-telemetry/opentelemetry-dotnet/pull/533"},{"type":"FIX","url":"https://github.com/open-telemetry/opentelemetry-dotnet/pull/7061"},{"type":"WEB","url":"https://github.com/open-telemetry/opentelemetry-dotnet/pull/3533"},{"type":"PACKAGE","url":"https://github.com/open-telemetry/opentelemetry-dotnet"},{"type":"WEB","url":"https://github.com/open-telemetry/opentelemetry-dotnet/releases/tag/core-1.15.3"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-29T11:31:04.000089971Z"}}