How severe is CVE-2026-123817?

No CVSS score has been assigned to CVE-2026-123817 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-123817?

CVE-2026-123817 affects the following packages: aiohttp (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2026-123817?

Update aiohttp to 3.14.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-123817 is resolved across your whole dependency graph.

How do I detect CVE-2026-123817 in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for aiohttp, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-123817 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2026-123817 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-123817 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What type of vulnerability is CVE-2026-123817?

CVE-2026-123817 is classified as CWE-770 (CWE-770). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-123817 published, and has it been updated?

CVE-2026-123817 was published on October 19, 2026 and was last updated on October 19, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍 PyPI

Not in CISA KEV

CVE-2026-123817 — aiohttp

Fix: aio-libs/aiohttp@09bcaa7

CVE-2026-123817 is a CWE-770 vulnerability in aiohttp. A fix is available for aiohttp — see the affected versions and patch details below.

aiohttp: Multiple instances of excessive or unbounded memory/CPU use

Published

Oct 19, 2026

Updated

Oct 19, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 19, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Real-World Exposure

1 pkg affected

🐍aiohttp

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to 3.14.4, the WebSocket reader retains one bytes object for each transport read while reassembling an incomplete frame. A malicious peer can split a frame into many tiny reads so per-object overhead substantially exceeds the payload bytes allowed by max_msg_size. The condition affects a server receiving frames from a malicious client and a client receiving frames from a malicious server, and can cause excessive memory consumption or denial of service. This issue is fixed in version 3.14.4.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`aiohttp`	all versions	3.14.4`pip install --upgrade 'aiohttp==3.14.4'`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for aiohttp, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update aiohttp to 3.14.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-123817 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Frequently Asked Questions

### Summary Multiple cases were found where aiohttp could use excessive or unbounded memory, or excessive CPU consumption on attacker controlled requests. ### Impact An attacker could cause resource exhaustion through specially crafted requests.

O3 Security · Impact-Aware SCA

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