# CVE-2021-28905: Denial of service in n/a

> A reachable assertion failure in libyang allows attackers to cause a denial of service by triggering a null pointer condition in node freeing.

- **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:** 20 May 2021
- **Updated:** 3 Aug 2024
- **Also known as:** DEBIAN-CVE-2021-28905, GHSA-qj7j-m28f-g68x, SUSE-SU-2022:2922-1, UBUNTU-CVE-2021-28905

## What is CVE-2021-28905?

CVE-2021-28905 is a high-severity denial of service vulnerability in n/a, published on 20 May 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In function lys_node_free() in libyang <= v1.0.225, it asserts that the value of node->module can't be NULL. But in some cases, node->module can be null, which triggers a reachable assertion (CWE-617).

Weakness: CWE-617 (Reachable Assertion)

## Which versions are affected by CVE-2021-28905?

It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `libyang` | SUSE:Linux Enterprise Module for Server Applications 15 SP3 | All versions | 1.0.184-150300.3.3.1 |
| `libyang` | SUSE:Linux Enterprise Module for Server Applications 15 SP4 | All versions | 1.0.184-150300.3.3.1 |
| `libyang` | openSUSE:Leap 15.3 | All versions | 1.0.184-150300.3.3.1 |
| `libyang` | openSUSE:Leap 15.4 | All versions | 1.0.184-150300.3.3.1 |

Products: Cesnet Libyang.

## How do I fix CVE-2021-28905?

Upgrade to a fixed version.

## Is CVE-2021-28905 being exploited?

There is no known exploitation of CVE-2021-28905 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2019-20393](https://insights.sbomify.com/CVE-2019-20393/): Memory corruption in n/a (high 8.8)
- [CVE-2019-20394](https://insights.sbomify.com/CVE-2019-20394/): Use after free in n/a (high 8.8)
- [CVE-2019-20397](https://insights.sbomify.com/CVE-2019-20397/): Memory corruption in n/a (high 8.8)
- [CVE-2019-19333](https://insights.sbomify.com/CVE-2019-19333/): Memory corruption in libyang (high 8.1)
- [CVE-2019-19334](https://insights.sbomify.com/CVE-2019-19334/): Memory corruption in libyang (high 8.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-28905 and fix it if it is affected.

What it is: CVE-2021-28905 is a high-severity denial of service vulnerability in n/a, published on 20 May 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-2021-28905 in the wild and no public exploit code.

Affected product: n/a. 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-2021-28905/ (Markdown: https://insights.sbomify.com/CVE-2021-28905/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-28905
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-28905
- OSV: https://osv.dev/vulnerability/CVE-2021-28905

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-28905/
Summaries are generated and may contain mistakes; the official description above is the record.