# CVE-2026-70666: Lemur: Server-Side Request Forgery via the ACME client following server-controlled URLs

> An attacker with authority-role access can redirect ACME client requests to internal services or cloud metadata endpoints via server-controlled URLs.

- **Severity:** High 7.4 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 Aug 2026
- **Updated:** 19 Aug 2026
- **Also known as:** GHSA-xpmj-wjcp-6pww, PYSEC-2026-3680

## What is CVE-2026-70666?

CVE-2026-70666 is a high-severity server-side request forgery vulnerability in Netflix lemur, published on 18 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Lemur manages TLS certificate creation. Prior to 1.9.3, an authority-role member could update acme_url through PUT /api/1/authorities/ without revalidation and direct setup_acme_client_no_retry to an attacker-controlled ACME server. ACME directory and order responses contain newNonce, newOrder, authorizations, and finalize URLs chosen by that server. The Lemur ClientV2 followed those URLs without requiring their host to match the configured directory host, allowing JWS-signed requests to internal services or cloud metadata endpoints. The issue required an ACME authority and a user authorized for that authority, but did not require global administrator privileges. The fix revalidates updates and introduces _PinnedClientNetwork to enforce a single allowed host for the complete ACME flow. This issue is fixed in version 1.9.3.

Weakness: CWE-918 (Server-Side Request Forgery)

## Which versions are affected by CVE-2026-70666?

3 open source packages ship an affected version, including lemur.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `lemur` | PyPI | All versions | 1.9.3 |
| `lemur` | PyPI | All versions | 1.9.3 |
| `lemur` | PyPI | All versions | 1.9.3 |

## How do I fix CVE-2026-70666?

Upgrade lemur to 1.9.3 or later.

## Is CVE-2026-70666 being exploited?

There is no known exploitation of CVE-2026-70666 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-70666 and fix it if it is affected.

What it is: CVE-2026-70666 is a high-severity server-side request forgery vulnerability in Netflix lemur, published on 18 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-70666 in the wild and no public exploit code.

Affected packages and fixed versions:
- lemur (PyPI): affected all versions; fixed in 1.9.3
- lemur (PyPI): affected all versions; fixed in 1.9.3
- lemur (PyPI): affected all versions; fixed in 1.9.3

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-2026-70666/ (Markdown: https://insights.sbomify.com/CVE-2026-70666/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-70666
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-70666
- OSV: https://osv.dev/vulnerability/CVE-2026-70666

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-70666/
Summaries are generated and may contain mistakes; the official description above is the record.