CVE-2025-69228: 
Wolfi vulnerability analysis and mitigation

CVE-2025-69228 is a Denial of Service vulnerability in AIOHTTP, an asynchronous HTTP client/server framework for asyncio and Python, caused by uncontrolled memory allocation when processing crafted multipart POST requests. It affects all versions of aiohttp up to and including 3.13.2, and was disclosed on January 5, 2026, with a fix released in version 3.13.3. The vulnerability carries a CVSS v3.1 base score of 7.5 (High) and a CVSS v4.0 base score of 6.6 (Medium) (GitHub Advisory, Red Hat Bugzilla).

The root cause is classified as CWE-770 (Allocation of Resources Without Limits or Throttling). Specifically, the size variable tracking multipart field sizes in the Request.post() method was incorrectly reset to zero at the start of each loop iteration rather than being initialized once before the loop, meaning the cumulative size check against client_max_size was never effectively enforced across multiple multipart fields. An unauthenticated remote attacker can craft a multipart POST request with many fields or oversized payloads targeting any endpoint that calls Request.post(), causing the server's memory to grow unboundedly until the process is frozen or killed. The fix (commit b7dbd35) moves the size = 0 initialization outside the while loop so that the total accumulated size of all multipart fields is correctly compared against the configured limit (GitHub Commit, GitHub Advisory).

Successful exploitation results in complete availability loss for the affected aiohttp server process — the server's memory fills up uncontrollably, effectively freezing or crashing the service and denying access to all legitimate users. There is no impact on confidentiality or integrity; the attack is purely a Denial of Service. Applications built on aiohttp that expose any endpoint using Request.post() for multipart form handling are at risk, and the impact extends to downstream users and services depending on the affected server (GitHub Advisory, Red Hat Bugzilla).

No public proof-of-concept exploit code or in-the-wild exploitation has been reported as of the time of writing. The vulnerability requires no authentication, no special privileges, and no user interaction, making it trivially exploitable by any network-accessible attacker against a vulnerable endpoint. The EPSS score is approximately 0.042–0.069%, indicating a low but non-negligible probability of exploitation in the near term. The vulnerability is not currently listed in the CISA Known Exploited Vulnerabilities (KEV) catalog (GitHub Advisory).

1. Reconnaissance: Identify internet-facing services running aiohttp versions ≤ 3.13.2 using banner grabbing, Shodan, or Censys. Look for Python/aiohttp in HTTP response headers.
2. Identify target endpoint: Locate an application endpoint that processes multipart form data (i.e., calls Request.post() internally), such as file upload or form submission handlers.
3. Craft malicious multipart POST request: Construct an HTTP POST request with Content-Type: multipart/form-data containing either a very large number of fields or individual fields with extremely large payloads, designed to bypass the per-field size reset bug.
4. Send the request: Transmit the crafted request to the target endpoint using tools such as curl, requests (Python), or a custom script. The server will begin buffering the multipart data into memory without enforcing the cumulative size limit.
5. Exhaust server memory: Repeat or sustain the request (or send multiple concurrent requests) to accelerate memory exhaustion, causing the aiohttp server process to freeze or crash, resulting in a denial of service for all users (GitHub Advisory, GitHub Commit).

• Network: Unusually large or numerous HTTP POST requests to endpoints that accept multipart form data; requests with abnormally high Content-Length values or many multipart boundary segments from a single or small set of source IPs.
• Logs: Aiohttp access logs showing repeated large POST requests to the same endpoint in a short time window; application logs showing memory-related errors or OOM (Out of Memory) conditions.
• Process: Rapid and sustained growth in the aiohttp server process's memory consumption (observable via top, htop, or system monitoring tools); server process becoming unresponsive or terminating unexpectedly.
• System: OS-level OOM killer events in /var/log/syslog or dmesg output referencing the Python/aiohttp process; sudden service unavailability coinciding with high memory usage.

The primary remediation is to upgrade aiohttp to version 3.13.3 or later, which enforces client_max_size correctly across the entire multipart form rather than resetting the counter per field. As a temporary workaround, operators can place a reverse proxy (e.g., nginx or HAProxy) in front of the aiohttp application and configure strict request body size limits at the proxy layer to reject oversized multipart requests before they reach the application. Additionally, rate-limiting POST requests at the network or application layer can reduce the risk of exploitation. IBM has also released patches for affected products including watsonx Orchestrate, Guardium Data Security Center, and Instana Observability (GitHub Advisory, IBM watsonx Advisory, IBM Guardium Advisory, IBM Instana Advisory).

The vulnerability was reported by security researchers ThomasRinsma and Finder16, with remediation developed by Dreamsorcerer from the aiohttp maintainer team (GitHub Advisory). Security news outlet SecurityOnline.info covered the disclosure as part of a broader report on seven vulnerabilities patched in aiohttp, highlighting the high-severity DoS risks. Red Hat, IBM, SUSE, Ubuntu, Debian, Splunk, and Dell have all issued advisories or patches for their products that bundle aiohttp, indicating broad industry awareness and response to this vulnerability.