high CVSS 7.5 EPSS 0.34%

CVE-2025-69227·Python vulnerability

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Versions 3.13.2 and below allow for an infinite loop to occur when assert statements are bypassed, resulting in a DoS attack when processing a POST body. If optimizations are enabled (-O or PYTHONOPTIMIZE=1), and the application includes a handler that uses the Request.post() method, then an attacker may be able to execute a DoS attack with a specially crafted message. This issue is fixed in version 3.13.3.

Severity
high
Software
Python
Fixed in
3.13.3
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at 0.34% — higher than 25% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Read the two together. CVE-2025-69227 scores 7.5 on CVSS, so a successful attack would be serious — but at 0.34%, almost nobody is currently attempting it. That is a different situation from a flaw under mass exploitation, and it is usually the difference between patching on your next maintenance window and patching tonight.

Affected versions

Until: 3.13.3

Fixed in: 3.13.3

How to fix this CVE

Upgrade AIOHTTP to version 3.13.3 or later to patch a denial-of-service vulnerability in POST request handling that occurs when Python optimizations are enabled. The vulnerability allows attackers to trigger an infinite loop by sending specially crafted POST bodies to applications using the Request.post() method, causing service unavailability. Update your Python packages immediately and verify the fix is deployed before resuming production traffic.

sudo dnf update python3-aiohttp

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

POST /[endpoint] HTTP/1.1 with Content-Length set but body contains crafted binary payloads designed to bypass assertion checks; observed in access logs as single requests causing sustained 100% CPU usage followed by application hang or timeout

WAF mitigation (if patching is not yet possible)

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

Implement rate limiting on POST endpoints and enforce Content-Length validation; additionally, configure WAF to block POST requests from untrusted sources until AIOHTTP is upgraded to 3.13.3+

How to check if you are affected

  1. Step 1: Check installed AIOHTTP version with `python3 -c "import aiohttp; print(aiohttp.__version__)"`
  2. Step 2: Verify Python is running with optimizations enabled by checking your startup process: `grep -E 'PYTHONOPTIMIZE|python.*-O' /proc/[pid]/environ`
  3. Step 3: Search application logs for POST request handlers that use Request.post() and correlate with sudden CPU spikes or service hangs: `grep -i 'request.post\|aiohttp.*post' /var/log/app/*.log | head -20`
  4. Step 4: After patching, confirm the new version with `python3 -c "import aiohttp; print(aiohttp.__version__)"` and validate version >= 3.13.3

FAQ

What is CVE-2025-69227?

CVE-2025-69227 is a denial-of-service vulnerability in AIOHTTP versions 3.13.2 and earlier that causes an infinite loop when processing POST request bodies in environments with Python optimizations enabled, allowing attackers to exhaust server resources and crash the application.

Is CVE-2025-69227 being actively exploited?

No, CVE-2025-69227 is not currently listed in CISA's Known Exploited Vulnerabilities catalog and no public exploits are available, though the attack requires minimal complexity to trigger.

What versions of Python are affected by CVE-2025-69227?

AIOHTTP versions up to and including 3.13.2 are vulnerable when running on Python with optimization flags enabled (-O or PYTHONOPTIMIZE=1). The vulnerability is fixed in AIOHTTP 3.13.3 and later.

How do I check if my server is vulnerable to CVE-2025-69227?

Run `python3 -c "import aiohttp; print('Vulnerable' if aiohttp.__version__ < '3.13.3' else 'Patched')"` and confirm Python optimizations are active with `python3 -O -c "import sys; print('OPTIMIZED' if sys.flags.optimize else 'NOT OPTIMIZED')"`.

Does Defensia detect CVE-2025-69227?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If AIOHTTP is installed on a monitored server, CVE-2025-69227 will appear in your dashboard with remediation steps.

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References

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