# CVE-2023-31137: MaraDNS Integer Underflow Vulnerability in DNS Packet Decompression

> A remote attacker can cause a Denial of Service in MaraDNS by sending a crafted DNS packet that triggers an integer underflow and abnormal program termination.

- **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 May 2023
- **Updated:** 13 Feb 2025
- **Also known as:** DEBIAN-CVE-2023-31137, GHSA-58m7-826v-9c3c, UBUNTU-CVE-2023-31137

## What is CVE-2023-31137?

CVE-2023-31137 is a high-severity vulnerability in Debian Debian Linux, published on 9 May 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

MaraDNS is open-source software that implements the Domain Name System (DNS). In version 3.5.0024 and prior, a remotely exploitable integer underflow vulnerability in the DNS packet decompression function allows an attacker to cause a Denial of Service by triggering an abnormal program termination.

The vulnerability exists in the `decomp_get_rddata` function within the `Decompress.c` file. When handling a DNS packet with an Answer RR of qtype 16 (TXT record) and any qclass, if the `rdlength` is smaller than `rdata`, the result of the line `Decompress.c:886` is a negative number `len = rdlength - total;`. This value is then passed to the `decomp_append_bytes` function without proper validation, causing the program to attempt to allocate a massive chunk of memory that is impossible to allocate. Consequently, the program exits with an error code of 64, causing a Denial of Service.

One proposed fix for this vulnerability is to patch `Decompress.c:887` by breaking `if(len <= 0)`, which has been incorporated in version 3.5.0036 via commit bab062bde40b2ae8a91eecd522e84d8b993bab58.

Weakness: CWE-191 (Integer Underflow (Wrap or Wraparound))

## Which versions are affected by CVE-2023-31137?

It affects 3 products.


Products: Debian Debian Linux, Fedoraproject Fedora, Maradns Maradns.

## How do I fix CVE-2023-31137?

Apply the vendor's patch.

## Is CVE-2023-31137 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2023-31137 exists.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
- [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild)
- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-31137 and fix it if it is affected.

What it is: CVE-2023-31137 is a high-severity vulnerability in Debian Debian Linux, published on 9 May 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2023-31137 exists.

Affected product: Debian Debian Linux. 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-2023-31137/ (Markdown: https://insights.sbomify.com/CVE-2023-31137/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-31137
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-31137
- OSV: https://osv.dev/vulnerability/CVE-2023-31137

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-31137/
Summaries are generated and may contain mistakes; the official description above is the record.