# CVE-2021-33913: Memory corruption in n/a

> Remote attackers can execute arbitrary code via a crafted SPF DNS record due to a heap-based buffer overflow in the libspf2 library.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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:** 19 Jan 2022
- **Updated:** 4 Aug 2024
- **Also known as:** ALPINE-CVE-2021-33913, DEBIAN-CVE-2021-33913, GHSA-7659-433m-4fhx, UBUNTU-CVE-2021-33913

## What is CVE-2021-33913?

CVE-2021-33913 is a critical memory corruption vulnerability in n/a, published on 19 Jan 2022. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

libspf2 before 1.2.11 has a heap-based buffer overflow that might allow remote attackers to execute arbitrary code (via an unauthenticated e-mail message from anywhere on the Internet) with a crafted SPF DNS record, because of SPF_record_expand_data in spf_expand.c. The amount of overflowed data depends on the relationship between the length of an entire domain name and the length of its leftmost label. The vulnerable code may be part of the supply chain of a site's e-mail infrastructure (e.g., with additional configuration, Exim can use libspf2; the Postfix web site links to unofficial patches for use of libspf2 with Postfix; older versions of spfquery relied on libspf2) but most often is not.

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

## Which versions are affected by CVE-2021-33913?

It affects 1 product.


Products: Libspf2 Project Libspf2.

## How do I fix CVE-2021-33913?

Upgrade to a fixed version.

## Is CVE-2021-33913 being exploited?

There is no known exploitation of CVE-2021-33913 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2023-42118](https://insights.sbomify.com/CVE-2023-42118/): Exim libspf2 Integer Underflow Remote Code Execution Vulnerability (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-33913 and fix it if it is affected.

What it is: CVE-2021-33913 is a critical memory corruption vulnerability in n/a, published on 19 Jan 2022. 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-2021-33913 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-2021-33913/ (Markdown: https://insights.sbomify.com/CVE-2021-33913/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-33913
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-33913
- OSV: https://osv.dev/vulnerability/CVE-2021-33913

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-33913/
Summaries are generated and may contain mistakes; the official description above is the record.