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Fencer Vulns
high 7.5

CVE-2026-34516 json

AIOHTTP: Multipart Header Size Bypass

published 2026-04-01 7 mo ago modified 2026-10-26 14 d ago also EUVD-2026-18040 , GHSA-m5qp-6w8w-w647 , PYSEC-2026-2098

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 39%
public exploits
0
none known

Summary

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.13.4, a response with an excessive number of multipart headers may be allowed to use more memory than intended, potentially allowing a DoS vulnerability. This issue has been patched in version 3.13.4.

Patch / fix

  • pypi aiohttp 3.13.4
  • aiohttp aiohttp 3.13.4
  • python-aiohttp Debian 12 3.8.4-1+deb12u2
  • python-aiohttp Debian 14 3.13.5-1

debian advisories DEBIAN-CVE-2026-34516

  • python-aiohttp Ubuntu Pro 16.04 LTS 0.20.2-1ubuntu0.1~esm1
  • python-aiohttp Ubuntu Pro 18.04 LTS 3.0.1-1ubuntu0.1~esm7
  • python-aiohttp Ubuntu Pro 22.04 LTS 3.8.1-4ubuntu0.2+esm3
  • python-aiohttp Ubuntu Pro 24.04 LTS 3.9.1-1ubuntu0.1+esm3
  • python-aiohttp Ubuntu Pro 26.04 LTS 3.13.3-3ubuntu1+esm1

ubuntu advisories UBUNTU-CVE-2026-34516

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • python-aiohttp SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES for SAP 15 SP4 +9 more 3.9.3-150400.10.43.1
  • python-aiohttp SLE Module for Public Cloud 15 SP7, SLE Module for Public Cloud 15 SP6, SLE Module for Public Cloud 15 SP5 +1 more 3.6.0-150100.3.35.1
  • python-aiohttp SLES for SAP applications 16.0, SLES 16.0 3.11.16-160000.5.1

suse advisories SUSE-SU-2026:3207-1SUSE-SU-2026:3059-1SUSE-SU-2026:22173-1

  • python-aiohttp openSUSE Leap 16.0 3.11.16-160000.5.1
  • python-aiohttp openSUSE Tumbleweed 3.13.5-3.1

opensuse advisories openSUSE-SU-2026:21098-1openSUSE-SU-2026:10545-1

  • py3-aiohttp Alpine 3.24, Alpine 3.23 3.13.5-r0

alpine advisories ALPINE-CVE-2026-34516

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-34516 updated cvss 5.3

aiohttp: AIOHTTP: Denial of Service via excessive multipart headers

  • Red Hat Lightspeed Core lightspeed-core/rag-tool-rhel9, lightspeed-core/lightspeed-stack-rhel9 Red Hat OpenShift Lightspeed openshift-lightspeed/lightspeed-ocp-rag-rhel9, openshift-lightspeed/lightspeed-service-api-rhel9, openshift-lightspeed-tech-preview/lightspeed-rag-tool-rhel9 Red Hat AI Inference Server rhaiis/vllm-cpu-rhel9, rhaiis/vllm-tpu-rhel9, rhaiis/vllm-cuda-rhel9, rhaiis/vllm-rocm-rhel9, rhaiis/vllm-spyre-rhel9, rhaiis/vllm-neuron-rhel9, +2 more Red Hat Ansible Automation Platform 2 automation-controller, ansible-automation-platform-26/hub-rhel9, ansible-automation-platform-24/lightspeed-rhel8, ansible-automation-platform-25/de-minimal-rhel8, ansible-automation-platform-25/de-minimal-rhel9, ansible-automation-platform-25/lightspeed-rhel8, +11 more Red Hat Ansible Automation Platform Ansible Core 2 ansible-automation-platform/ee-minimal-rhel8, ansible-automation-platform/ee-minimal-rhel9, ansible-automation-platform-tech-preview/ee-minimal-rhel8, ansible-automation-platform-tech-preview/ee-minimal-rhel9 Red Hat Enterprise Linux AI (RHEL AI) 3 rhelai3/bootc-cuda-rhel9, rhelai3/bootc-rocm-rhel9, rhelai3/bootc-aws-cuda-rhel9, rhelai3/bootc-gcp-cuda-rhel9, rhelai3/bootc-azure-cuda-rhel9, rhelai3/bootc-azure-rocm-rhel9
    +2 more products
    Red Hat OpenShift AI (RHOAI) rhoai/odh-mlflow-rhel9, rhoai/odh-mlserver-rhel9, rhoai/odh-vllm-cpu-rhel9, rhoai/odh-vllm-cuda-rhel9, rhoai/odh-vllm-rocm-rhel9, rhoai/odh-caikit-nlp-rhel9, +40 more Red Hat Satellite 6 satellite/iop-insights-engine-rhel9, satellite/iop-vulnerability-engine-rhel9
    affected: workaround, no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
7 mo ago

Exploit prediction

0.46% chance of exploitation in the next 30 days, higher than 39% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 4.0 6.6 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U
CISA ADP 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
GitHub 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CNA 4.0 6.6 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
pypi aiohttp
<3.13.4
3.13.4

Affected products

  • aio-libs aiohttp

Classification

Weakness
  • CWE-770 Allocation of Resources Without Limits or Throttling

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.