# CVE-2006-0743: Apache log4net format string vulnerability causes DoS

> Remote attackers can cause denial of service via memory corruption in the LocalSyslogAppender component of the log4net library.

- **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:** 9 Mar 2006
- **Updated:** 7 Aug 2024
- **Also known as:** GHSA-f9fr-w54q-772h, openSUSE-SU-2024:10072-1

## What is CVE-2006-0743?

CVE-2006-0743 is a medium-severity memory corruption vulnerability in n/a, published on 9 Mar 2006. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Format string vulnerability in LocalSyslogAppender in Apache log4net 1.2.9 might allow remote attackers to cause a denial of service (memory corruption and termination) via unknown vectors.

Weakness: CWE-134 (Use of Externally-Controlled Format String)

## Which versions are affected by CVE-2006-0743?

2 open source packages ship an affected version, including log4net. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `log4net` | NuGet | All versions | 1.2.10 |
| `log4net` | NuGet | All versions | 1.2.10 |
| `log4net` | openSUSE:Tumbleweed | All versions | 1.2.10-75.6 |

Products: Apache Log4net.

## How do I fix CVE-2006-0743?

Upgrade log4net to 1.2.10 or later.

## Is CVE-2006-0743 being exploited?

There is no known exploitation of CVE-2006-0743 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2018-1285](https://insights.sbomify.com/CVE-2018-1285/): XML External Entity attack in log4net (critical 9.8)
- [CVE-2026-40021](https://insights.sbomify.com/CVE-2026-40021/): Apache Log4net: Silent log event loss in XmlLayout and XmlLayoutSchemaLog4J due to unescaped XML 1.0 forbidden characters (medium 6.3)
- [CVE-2026-105239](https://insights.sbomify.com/CVE-2026-105239/): Apache log4net: NUL character truncates EventLogAppender records (medium 5.3)
- [CVE-2026-105240](https://insights.sbomify.com/CVE-2026-105240/): Apache log4net: NUL character truncates OutputDebugStringAppender records (medium 5.3)
- [CVE-2026-105241](https://insights.sbomify.com/CVE-2026-105241/): Apache log4net: Unencodable content discards a whole SmtpPickupDirAppender batch (medium 5.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2006-0743 and fix it if it is affected.

What it is: CVE-2006-0743 is a medium-severity memory corruption vulnerability in n/a, published on 9 Mar 2006. 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-2006-0743 in the wild and no public exploit code.

Affected packages and fixed versions:
- log4net (NuGet): affected all versions; fixed in 1.2.10
- log4net (NuGet): affected all versions; fixed in 1.2.10

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-2006-0743/ (Markdown: https://insights.sbomify.com/CVE-2006-0743/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2006-0743
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2006-0743
- OSV: https://osv.dev/vulnerability/CVE-2006-0743

---
From sbomify Insights: https://insights.sbomify.com/CVE-2006-0743/
Summaries are generated and may contain mistakes; the official description above is the record.