# CVE-2021-21257: Out-of-bounds write in RPL-Classic and RPL-Lite

> Attackers can trigger out-of-bounds writes via crafted RPL packets in Contiki-NG, potentially leading to code execution or denial of service.

- **Severity:** High 8.2 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 18 Jun 2021
- **Updated:** 3 Aug 2024

## What is CVE-2021-21257?

CVE-2021-21257 is a high-severity memory corruption vulnerability in contiki-ng, published on 18 Jun 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Contiki-NG is an open-source, cross-platform operating system for internet of things devices. The RPL-Classic and RPL-Lite implementations in the Contiki-NG operating system versions prior to 4.6 do not validate the address pointer in the RPL source routing header This makes it possible for an attacker to cause out-of-bounds writes with packets injected into the network stack. Specifically, the problem lies in the rpl_ext_header_srh_update function in the two rpl-ext-header.c modules for RPL-Classic and RPL-Lite respectively. The addr_ptr variable is calculated using an unvalidated CMPR field value from the source routing header. An out-of-bounds write can be triggered on line 151 in os/net/routing/rpl-lite/rpl-ext-header.c and line 261 in os/net/routing/rpl-classic/rpl-ext-header.c, which contain the following memcpy call with addr_ptr as destination. The problem has been patched in Contiki-NG 4.6. Users can apply a patch out-of-band as a workaround.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2021-21257?

It affects 1 product.


Products: Contiki-Ng Contiki-Ng.

## How do I fix CVE-2021-21257?

No fix has been published for CVE-2021-21257 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-21257 being exploited?

There is no known exploitation of CVE-2021-21257 in the wild and no public exploit code.

## Other vulnerabilities in contiki-ng

- [CVE-2018-19417](https://insights.sbomify.com/CVE-2018-19417/): Memory corruption in n/a (critical 10.0)
- [CVE-2023-30546](https://insights.sbomify.com/CVE-2023-30546/): Contiki-NG has off-by-one error in Antelope DBMS (critical 9.8)
- [CVE-2020-24336](https://insights.sbomify.com/CVE-2020-24336/): Memory corruption in n/a (critical 9.8)
- [CVE-2020-14934](https://insights.sbomify.com/CVE-2020-14934/): Memory corruption in n/a (critical 9.8)
- [CVE-2020-14935](https://insights.sbomify.com/CVE-2020-14935/): Memory corruption in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-21257 and fix it if it is affected.

What it is: CVE-2021-21257 is a high-severity memory corruption vulnerability in contiki-ng, published on 18 Jun 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-2021-21257 in the wild and no public exploit code.

Affected product: contiki-ng. 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-2021-21257/ (Markdown: https://insights.sbomify.com/CVE-2021-21257/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21257
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21257
- OSV: https://osv.dev/vulnerability/CVE-2021-21257

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-21257/
Summaries are generated and may contain mistakes; the official description above is the record.