# CVE-2011-1756: Denial of service in n/a

> Remote attackers can cause denial of service in Citadel mail server via crafted XML with nested entity references, consuming memory and CPU.

- **Severity:** Medium 5.0 (`AV:N/AC:L/Au:N/C:N/I:N/A:P`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 21 Jun 2011
- **Updated:** 6 Aug 2024
- **Also known as:** DSA-2250-1, GHSA-6px8-r2g4-9v5v

## What is CVE-2011-1756?

CVE-2011-1756 is a medium-severity denial of service vulnerability in n/a, published on 21 Jun 2011. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

modules/xmpp/serv_xmpp.c in Citadel 7.86 and earlier does not properly detect recursion during entity expansion, which allows remote attackers to cause a denial of service (memory and CPU consumption) via a crafted XML document containing a large number of nested entity references, a similar issue to CVE-2003-1564.

Weakness: CWE-399

## Which versions are affected by CVE-2011-1756?

It affects 1 product.


Products: Citadel Citadel.

## How do I fix CVE-2011-1756?

Upgrade to a fixed version.

## Is CVE-2011-1756 being exploited?

There is no known exploitation of CVE-2011-1756 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2023-44272](https://insights.sbomify.com/CVE-2023-44272/): Cross-site scripting in Citadel (medium 5.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2011-1756 and fix it if it is affected.

What it is: CVE-2011-1756 is a medium-severity denial of service vulnerability in n/a, published on 21 Jun 2011. 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-2011-1756 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-2011-1756/ (Markdown: https://insights.sbomify.com/CVE-2011-1756/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2011-1756
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2011-1756
- OSV: https://osv.dev/vulnerability/CVE-2011-1756

---
From sbomify Insights: https://insights.sbomify.com/CVE-2011-1756/
Summaries are generated and may contain mistakes; the official description above is the record.