AIOHTTP WebSocket frame reassembly permits excessive memory consumption from tiny reads
Affects aiohttp 3.14.3 and earlier when a WebSocket frame arrives split across many small transport reads. Fixed in 3.14.4.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- Fixed in 3.14.4
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 3.14.4.
- Last modified
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 26/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Unclear
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
AIOHTTP, an asynchronous HTTP client and server framework for Python, can be made to consume excessive memory through its WebSocket frame reassembly, which can lead to denial of service. An attacker can trigger this remotely, without logging in, by sending a frame split into many tiny reads.
Read the original 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.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure17/25No login or user action needed, reachable over the network without a login · Unknown: Advisories don't say whether default setups are affected
- Reach?/20Unknown. No tracked technology or package matched
- Severity8.7/10CVSS 8.7
- No patch0/5No signal
What would change the score
- Would score about 71 if added to CISA KEV
- Would score about 66 if CISA's SSVC rates exploitation active
- Would score about 31 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 3.14.4.
Timeline
- CVE published
- First seen by cve.now
Affected versions
- aio-libs aiohttp
fixed in 3.14.4
Evidence 6
- Advisory
- Repository
- Repository
- Repository
- Repository
- Repository
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-123817
Is CVE-2026-123817 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
What does this mean?
Reassembling a WebSocket frame that arrives in many tiny pieces uses far more memory than the payload size limit suggests, because of per-object overhead. This can cause excessive memory use in a WebSocket server or client, resulting in denial of service.Source: github.com
Which versions are affected by CVE-2026-123817?
aiohttp: before 3.14.4.Source: cve.now feed data
Am I affected, and how do I check?
aiohttp 3.14.3 and earlier are affected, in cases where WebSocket frames arrive split across many small transport reads. To check the installed version, run pip show aiohttp or python -c 'import aiohttp; print(aiohttp.__version__)'.Source: github.com
How do I fix CVE-2026-123817?
Upgrade aiohttp to 3.14.4 or later, which contains the fix.Source: github.com