# CVE-2021-43172: Infinite length chain of RRDP repositories

> A malicious CA can cause Routinator to hang indefinitely by creating an infinite chain of RRDP repositories, preventing validation completion.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 9 Nov 2021
- **Updated:** 16 Sep 2024
- **Also known as:** DEBIAN-CVE-2021-43172, GHSA-m3x9-623g-35c4, UBUNTU-CVE-2021-43172

## What is CVE-2021-43172?

CVE-2021-43172 is a high-severity denial of service vulnerability in NLnet Labs Routinator, published on 9 Nov 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

NLnet Labs Routinator prior to 0.10.2 happily processes a chain of RRDP repositories of infinite length causing it to never finish a validation run. In RPKI, a CA can choose the RRDP repository it wishes to publish its data in. By continuously generating a new child CA that only consists of another CA using a different RRDP repository, a malicious CA can create a chain of CAs of de-facto infinite length. Routinator prior to version 0.10.2 did not contain a limit on the length of such a chain and will therefore continue to process this chain forever. As a result, the validation run will never finish, leading to Routinator continuing to serve the old data set or, if in the initial validation run directly after starting, never serve any data at all.

Weakness: CWE-835 (Loop with Unreachable Exit Condition), CWE-674 (Uncontrolled Recursion)

## Which versions are affected by CVE-2021-43172?

2 open source packages ship an affected version, including routinator. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `routinator` | crates.io | All versions | 0.10.2 |
| `routinator` | crates.io | All versions | 0.10.2 |

Products: Nlnetlabs Routinator.

## How do I fix CVE-2021-43172?

Upgrade routinator to 0.10.2 or later.

## Is CVE-2021-43172 being exploited?

There is no known exploitation of CVE-2021-43172 in the wild and no public exploit code.

## Other vulnerabilities in NLnet Labs Routinator

- [CVE-2023-39916](https://insights.sbomify.com/CVE-2023-39916/): Possible path traversal when storing RRDP responses (critical 9.3)
- [CVE-2026-49235](https://insights.sbomify.com/CVE-2026-49235/): Routinator crashes on specifically crafted RRDP XML files (high 8.7)
- [CVE-2026-49233](https://insights.sbomify.com/CVE-2026-49233/): Routinator cache path traversal using rogue rsync URIs (high 8.3)
- [CVE-2026-49234](https://insights.sbomify.com/CVE-2026-49234/): Routinator crashes on specifically crafted ASN strings in the API (high 8.2)
- [CVE-2023-39915](https://insights.sbomify.com/CVE-2023-39915/): Crashes on parsing certain invalid RPKI objects (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-43172 and fix it if it is affected.

What it is: CVE-2021-43172 is a high-severity denial of service vulnerability in NLnet Labs Routinator, published on 9 Nov 2021. 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-2021-43172 in the wild and no public exploit code.

Affected packages and fixed versions:
- routinator (crates.io): affected all versions; fixed in 0.10.2
- routinator (crates.io): affected all versions; fixed in 0.10.2

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-2021-43172/ (Markdown: https://insights.sbomify.com/CVE-2021-43172/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-43172
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-43172
- OSV: https://osv.dev/vulnerability/CVE-2021-43172

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-43172/
Summaries are generated and may contain mistakes; the official description above is the record.