CVE-2026-54279Network attack vector

Cookie disclosure via lost host-only scope

Published Jun 22, 2026 · Updated Jun 22, 2026

Improper cookie scoping in aiohttp before 3.14.1 allows remote attackers to receive persisted host-only cookies through subdomain requests. CookieJar.save() omits the internal host-only marker, so CookieJar.load() reconstructs the cookie as a domain cookie eligible for subdomains. Exploitation requires an application to persist and reload a host-only cookie and then request an attacker-accessible subdomain, exposing that cookie's contents.

CVSS severity7.5
High
EPSS probability0.28%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper cookie scoping in aiohttp before 3.14.1 allows remote attackers to receive persisted host-only cookies through subdomain requests. CookieJar.save() omits the internal host-only marker, so CookieJar.load() reconstructs the cookie as a domain cookie eligible for subdomains. Exploitation requires an application to persist and reload a host-only cookie and then request an attacker-accessible subdomain, exposing that cookie's contents.

The record

CVE
CVE-2026-54279
Published
Jun 22, 2026
Updated
Jun 22, 2026
Vendor
aio-libs
Product
aiohttp
Classifications
CWE-665, T1539
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 22, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 22, 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=< 3.14.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

aio-libs · aiohttpversion=< 3.14.1

Published CVSS scores

7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
1.3GitHubCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:N/SA:N/E:U

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.

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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-665Improper Initialization
T1539Steal Web Session Cookie

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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