# CVE-2026-126360: OpenTelemetry Python: Denial of service through quadratic-time traceparent parsing in opentelemetry-api

> Attackers can send malformed traceparent headers causing quadratic regex backtracking, exhausting CPU on servers using OpenTelemetry Python.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Harmful if only installed:** No
- **Needs a specific call:** No
- **Fix available:** No
- **Published:** 12 Nov 2026
- **Updated:** 12 Nov 2026
- **Also known as:** GHSA-mf5v-w3w3-f6cg

## What is CVE-2026-126360?

CVE-2026-126360 is a medium-severity denial of service vulnerability in open-telemetry opentelemetry-python, published on 12 Nov 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

OpenTelemetry Python provides the Python API and SDK for OpenTelemetry. Prior to 1.45.2, TraceContextTextMapPropagator.extract() in opentelemetry-api can perform quadratic-time regular-expression backtracking on a malformed traceparent value containing a trace-context prefix, a long whitespace sequence, and an embedded newline. Exploitation requires an attacker-controlled carrier that preserves embedded newlines and permits a sufficiently large value, because conforming HTTP header values cannot contain embedded newlines. JSON-based carriers, including applicable MCP request metadata integrations, can preserve the required newline depending on the SDK, instrumentation, and message-size limits. Parsing on an asynchronous server's event-loop thread can consume excessive CPU and delay unrelated requests, while the advisory does not establish disclosure, modification, or code execution. This issue is fixed in version 1.45.2.

Weakness: CWE-1333 (Inefficient Regular Expression Complexity)

## Which versions are affected by CVE-2026-126360?

An affected version is exposed as installed. No special setting or call is needed.


## How do I fix CVE-2026-126360?

No fix has been published for CVE-2026-126360 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-126360 being exploited?

There is no known exploitation of CVE-2026-126360 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-126360 and fix it if it is affected.

What it is: CVE-2026-126360 is a medium-severity denial of service vulnerability in open-telemetry opentelemetry-python, published on 12 Nov 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-126360 in the wild and no public exploit code.
Exposure: An affected version is exposed as installed. No special setting or call is needed.

Affected product: open-telemetry opentelemetry-python. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-126360/ (Markdown: https://insights.sbomify.com/CVE-2026-126360/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-126360
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-126360
- OSV: https://osv.dev/vulnerability/CVE-2026-126360

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-126360/
Summaries are generated and may contain mistakes; the official description above is the record.