# CVE-2021-4097: CRLF Injection in phpservermon/phpservermon

> Attackers can inject CRLF sequences into phpservermon, potentially manipulating HTTP headers or log entries.

- **Severity:** Medium 6.3 (`CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 11 Dec 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-8qv8-fq5w-p966

## What is CVE-2021-4097?

CVE-2021-4097 is a medium-severity vulnerability in phpservermon/phpservermon, published on 11 Dec 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

phpservermon is vulnerable to Improper Neutralization of CRLF Sequences

Weakness: CWE-93 (Improper Neutralization of CRLF Sequences)

## Which versions are affected by CVE-2021-4097?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `phpservermon/phpservermon` | Packagist | All versions to 3.5.2 | None |
| `phpservermon/phpservermon` | Packagist | All versions to 3.5.2 | None |

Products: Phpservermonitor Php Server Monitor.

## How do I fix CVE-2021-4097?

No fix has been published for CVE-2021-4097 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-4097 being exploited?

There is no known exploitation of CVE-2021-4097 in the wild and no public exploit code.

## Other vulnerabilities in phpservermon/phpservermon

- [CVE-2018-18921](https://insights.sbomify.com/CVE-2018-18921/): CSRF in PHP Server Monitor before 3.3.2 (medium 6.5)
- [CVE-2021-4240](https://insights.sbomify.com/CVE-2021-4240/): phpservermon User.php generatePasswordResetToken predictable algorithm in random number generator (low 2.6)
- [CVE-2021-4241](https://insights.sbomify.com/CVE-2021-4241/): phpservermon User.php setUserLoggedIn predictable algorithm in random number generator (low 2.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-4097 and fix it if it is affected.

What it is: CVE-2021-4097 is a medium-severity vulnerability in phpservermon/phpservermon, published on 11 Dec 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-4097 in the wild and no public exploit code.

Affected packages and fixed versions:
- phpservermon/phpservermon (Packagist): affected all versions up to 3.5.2; no fix listed
- phpservermon/phpservermon (Packagist): affected all versions up to 3.5.2; no fix listed

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-2021-4097/ (Markdown: https://insights.sbomify.com/CVE-2021-4097/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-4097
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-4097
- OSV: https://osv.dev/vulnerability/CVE-2021-4097

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-4097/
Summaries are generated and may contain mistakes; the official description above is the record.