high CVSS 7.5

CVE-2026-50269·Python vulnerability

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to 3.14.0, attacker-controlled input included into multipart/payload headers can be used to modify a request to inject additional headers or similar. In the unlikely situation that an application is passing user-controlled strings into MultipartWriter.append(headers=...) or Payload.headers, then an attacker may be able to modify the request to inject headers or change the contents of the request. This vulnerability is fixed in 3.14.0.

Severity
high
Software
Python
Fixed in
3.14.0
Published
2026-06-22

Affected versions

Until: 3.14.0

Fixed in: 3.14.0

How to fix this CVE

Update AIOHTTP to version 3.14.0 or later to patch a header injection vulnerability in multipart request handling. If your application uses MultipartWriter or Payload with user-controlled header inputs, this update is critical to prevent request manipulation attacks. Verify the update by checking the installed AIOHTTP version after upgrading Python packages.

sudo dnf update python3-aiohttp

Defensia detects this vulnerability

WAF mitigation (if patching is not yet possible)

Add this rule to your WAF to block exploitation attempts while you schedule the patch. 

Implement strict input validation and sanitization for all multipart form headers before passing them to AIOHTTP's MultipartWriter or Payload objects. Reject or escape headers containing line-feed (LF: \n) or carriage-return (CR: \r) characters, which are commonly used in header injection attacks.

How to check if you are affected

  1. Step 1: Check AIOHTTP version with: python3 -c "import aiohttp; print(aiohttp.__version__)"
  2. Step 2: Identify if your application calls MultipartWriter.append(headers=...) or modifies Payload.headers with external input by searching your codebase: grep -r "MultipartWriter\|Payload.headers" /path/to/app/
  3. Step 3: Search application logs for unusual multipart request patterns or header-related errors around request boundaries: grep -i "multipart\|header.*inject\|content-disposition" /var/log/app.log
  4. Step 4: Verify the patch by confirming AIOHTTP version is >= 3.14.0 after update: python3 -c "import aiohttp; assert tuple(map(int, aiohttp.__version__.split('.'))) >= (3, 14, 0), 'Vulnerable version'"

FAQ

What is CVE-2026-50269?

CVE-2026-50269 is a header injection flaw in AIOHTTP's multipart request handling that allows attackers to inject or modify HTTP headers when user-controlled strings are passed directly to MultipartWriter or Payload header parameters.

Is CVE-2026-50269 being actively exploited?

No, CVE-2026-50269 is not listed on the CISA KEV catalog and no public exploits are currently available, though the vulnerability should still be remediated promptly as it requires specific application patterns to exploit.

What versions of Python are affected by CVE-2026-50269?

The vulnerability affects AIOHTTP prior to version 3.14.0 across all Python distributions. It is fixed in AIOHTTP 3.14.0 and later.

How do I check if my server is vulnerable to CVE-2026-50269?

Run: python3 -c "import aiohttp; print('Vulnerable' if tuple(map(int, aiohttp.__version__.split('.'))) < (3, 14, 0) else 'Patched')"

Does Defensia detect CVE-2026-50269?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If AIOHTTP is installed on a monitored server, CVE-2026-50269 will appear in your dashboard with remediation steps.

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References

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