CVE-2026-34516Network attack vector

Service interruption via unbounded multipart headers

Published Apr 1, 2026 · Updated Apr 1, 2026

Resource exhaustion in aiohttp before 3.13.4 allows remote attackers to consume excess memory through multipart messages with many headers. MultipartReader._read_headers reads each part's header lines into a list without applying the normal per-field size or header-count limits. Any client or server application that parses attacker-controlled multipart content is exposed; existing body limits constrain but do not eliminate service interruption.

CVSS severity7.5
High
EPSS probability0.44%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in aiohttp before 3.13.4 allows remote attackers to consume excess memory through multipart messages with many headers. MultipartReader._read_headers reads each part's header lines into a list without applying the normal per-field size or header-count limits. Any client or server application that parses attacker-controlled multipart content is exposed; existing body limits constrain but do not eliminate service interruption.

The record

CVE
CVE-2026-34516
Published
Apr 1, 2026
Updated
Apr 1, 2026
Vendor
aio-libs
Product
aiohttp
Classifications
CWE-770, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 1, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 1, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 3.13.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

aio-libs · aiohttpversion=< 3.13.4

Published CVSS scores

6.6GitHub, Inc.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
7.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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