Summary
AIOHTTP: WebSocket client accepts compressed frames without negotiated permessage-deflate
The client accepts and decompresses frames with the RSV1 bit set even when the permessage-deflate extension was not negotiated.
Impact
A client may unexpectedly decompress WebSocket frames when explicitly opted out. This could lead to additional CPU/memory consumption, but is unlikely to be a significant issue unless a zip bomb vulnerability or similar is also present.
Patch: https://github.com/aio-libs/aiohttp/commit/47fb6ae354d4fa22048f4dbe7dbf82b625f0a2f6
The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-59881? CVE-2026-59881 is a medium-severity improper input validation vulnerability in aiohttp (pip), affecting versions <= 3.14.1. It is fixed in 3.14.2. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
- Which versions of aiohttp are affected by CVE-2026-59881? aiohttp (pip) versions <= 3.14.1 is affected.
- Is there a fix for CVE-2026-59881? Yes. CVE-2026-59881 is fixed in 3.14.2. Upgrade to this version or later.
- Is CVE-2026-59881 exploitable, and should I be worried? Whether CVE-2026-59881 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-59881 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-59881? Upgrade
aiohttpto 3.14.2 or later.