# CVE-2026-9658: Plack::Middleware::Security::Common versions before 0.13.1 for Perl did not block header injections in request paths

> Attackers can inject headers via request paths in Plack::Middleware::Security::Common due to ineffective CRLF blocking, potentially bypassing security controls.

- **Severity:** High 7.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/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:** Not needed
- **Fix available:** No
- **Published:** 28 May 2026
- **Updated:** 1 Jun 2026
- **Also known as:** GHSA-xcq6-chp9-g954

## What is CVE-2026-9658?

CVE-2026-9658 is a high-severity vulnerability in RRWO Plack::Middleware::Security::Common, published on 28 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Plack::Middleware::Security::Common versions before 0.13.1 for Perl did not block header injections in request paths.

The header injection rule was ineffective at blocking header injections in the request paths unless they were double-encoded, for example,

  GET /path\r\nHTTP/1.1\r\nHost: secret.example.com

Note that it is unclear whether request paths with CRLF followed by additional headers would be blocked by reverse proxies, or how they would be processed by Plack-based servers.

Weakness: CWE-790 (Improper Filtering of Special Elements), CWE-113 (Improper Neutralization of CRLF Sequences in HTTP Headers)

## Which versions are affected by CVE-2026-9658?


## How do I fix CVE-2026-9658?

No fix has been published for CVE-2026-9658 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-9658 being exploited?

There is no known exploitation of CVE-2026-9658 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-9658 and fix it if it is affected.

What it is: CVE-2026-9658 is a high-severity vulnerability in RRWO Plack::Middleware::Security::Common, published on 28 May 2026. 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-2026-9658 in the wild and no public exploit code.

Affected product: RRWO Plack::Middleware::Security::Common. 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-2026-9658/ (Markdown: https://insights.sbomify.com/CVE-2026-9658/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-9658
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-9658
- OSV: https://osv.dev/vulnerability/CVE-2026-9658

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-9658/
Summaries are generated and may contain mistakes; the official description above is the record.