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How CVE-2026-69244 Works
The vulnerability resides in the C-based HTTP response parser component of the aiohttp library, specifically within the error message construction path for malformed chunked responses. When the parser encounters a malformed HTTP response—such as an invalid chunked encoding or malformed bytes at the buffer end—it attempts to build a diagnostic error snippet to aid debugging. To construct this snippet, the parser uses an error-position pointer returned by the underlying llhttp library.
The flaw arises because the code does not properly validate that this pointer falls within the bounds of the allocated heap buffer before dereferencing it. An attacker who controls a malicious server, or even an accidentally malformed response from a legitimate server, can trigger this out-of-bounds heap read. The read operation attempts to access memory beyond the buffer’s limits, which can lead to a crash or denial-of-service (DoS) in the client application. In some scenarios, this could also be combined with other attack vectors to potentially escalate privileges or leak memory contents.
All aiohttp versions prior to 3.14.3 are affected. The vulnerability is fixed in version 3.14.3 via a commit that introduces proper bounds checking before using the error-position pointer. As a workaround, users can disable the C parser entirely by setting the environment variable AIOHTTP_NO_EXTENSIONS=1, which forces the library to use the unaffected Python-based parser.
DailyCVE Form:
Platform: aio-libs/aiohttp
Version: < 3.14.3
Vulnerability: Out-of-bounds heap read
Severity: High (CVSS:7.1)
date: 2026-08-03
Prediction: 2026-08-10 (within 7 days)
What Undercode Say: Analytics
The vulnerability manifests specifically in `aiohttp/_http_parser.pyx` where the llhttp error-position pointer is used unsafely. The root cause is improper bounds checking when constructing error messages for malformed chunked responses or malformed bytes at buffer boundaries.
Detection & Verification Commands:
Check installed aiohttp version
python -c "import aiohttp; print(aiohttp.<strong>version</strong>)"
Verify if C extensions are in use (default on most installations)
python -c "import aiohttp._http_parser; print('C parser enabled')"
Test for vulnerability (requires a malicious server setup)
Example: send a malformed chunked response with invalid size encoding
curl -X GET http://malicious-server/ -H "Transfer-Encoding: chunked" --data-binary "0\r\n\r\nInvalid"
Check for the fix commit in your local source
git log --oneline | grep "49f65d5" Patch commit reference
Exploit:
An attacker sets up a malicious HTTP server that responds with a carefully crafted malformed chunked response. For example, the server could send a chunk size that is invalid or incomplete, causing the llhttp parser to return an error-position pointer that points outside the allocated heap buffer. When the aiohttp client processes this response, the error message construction code reads from this invalid pointer, leading to a crash or DoS. The exploit requires no authentication and can be triggered by any client that connects to the attacker-controlled server.
Protection:
- Upgrade to aiohttp 3.14.3 or later immediately.
- If an immediate upgrade is not possible, set the environment variable `AIOHTTP_NO_EXTENSIONS=1` before running your application to force the use of the Python parser, which is not affected.
- Apply the official patch commit: aio-libs/aiohttp@49f65d5.
- Consider using a Web Application Firewall (WAF) or reverse proxy to filter or normalize malformed HTTP responses before they reach the aiohttp client.
Impact:
- Denial of Service (DoS): An attacker can crash the client application, rendering it unavailable.
- Potential Memory Leak: Out-of-bounds reads could leak sensitive heap data if exploited in conjunction with other vulnerabilities.
- Wide Attack Surface: Any application using aiohttp to communicate with untrusted or external HTTP servers is at risk.
- CVSS Score: 7.1 (High) with Network attack vector, Low complexity, No privileges required, and Passive user interaction.
- Affected Versions: All releases prior to 3.14.3.
- CWE: CWE-125 (Out-of-bounds Read), CWE-400 (Uncontrolled Resource Consumption).
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Sources:
Reported By: github.com
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