# CVE-2020-12403: Memory corruption in nss

> Out-of-bounds reads in NSS CHACHA20-POLY1305 implementation allow attackers to compromise confidentiality and system availability.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/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:** 27 May 2021
- **Updated:** 4 Aug 2024
- **Also known as:** ALPINE-CVE-2020-12403, AZL-6746, DEBIAN-CVE-2020-12403, GHSA-9h25-47mw-52hh, UBUNTU-CVE-2020-12403, USN-4476-1

## What is CVE-2020-12403?

CVE-2020-12403 is a critical memory corruption vulnerability in nss, published on 27 May 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A flaw was found in the way CHACHA20-POLY1305 was implemented in NSS in versions before 3.55. When using multi-part Chacha20, it could cause out-of-bounds reads. This issue was fixed by explicitly disabling multi-part ChaCha20 (which was not functioning correctly) and strictly enforcing tag length. The highest threat from this vulnerability is to confidentiality and system availability.

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2020-12403?

It affects 1 product.


Products: Mozilla Nss.

## How do I fix CVE-2020-12403?

Upgrade to a fixed version.

## Is CVE-2020-12403 being exploited?

There is no known exploitation of CVE-2020-12403 in the wild and no public exploit code.

## Other vulnerabilities in nss

- [CVE-2021-43527](https://insights.sbomify.com/CVE-2021-43527/): Memory corruption in NSS (critical 9.8)
- [CVE-2023-4421](https://insights.sbomify.com/CVE-2023-4421/): Information disclosure in NSS (medium 6.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-12403 and fix it if it is affected.

What it is: CVE-2020-12403 is a critical memory corruption vulnerability in nss, published on 27 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-2020-12403 in the wild and no public exploit code.

Affected product: nss. 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-2020-12403/ (Markdown: https://insights.sbomify.com/CVE-2020-12403/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-12403
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-12403
- OSV: https://osv.dev/vulnerability/CVE-2020-12403

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-12403/
Summaries are generated and may contain mistakes; the official description above is the record.