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CVE-2026-34520

Aiohttp vulnerability

9.1 CRITICALEPSS 0.68%
  1. Published1 Apr 2026

Description

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.13.4, the C parser (the default for most installs) accepted null bytes and control characters in response headers. This issue has been patched in version 3.13.4.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityNone
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Affected products

Aiohttp< 3.13.4

Remediation

Fixed in
Aiohttp≥ 3.13.4

References

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Frequently asked

Is CVE-2026-34520 being actively exploited?

CVE-2026-34520 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.68%.

How severe is CVE-2026-34520?

CVE-2026-34520 has a CVSS 3.1 base score of 9.1, rated critical. EPSS estimates a 0.68% probability of exploitation.

Which products are affected by CVE-2026-34520?

Affected products include Aiohttp.

How do I fix CVE-2026-34520?

Upgrade affected software to a fixed version, for example Aiohttp 3.13.4 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-34520 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.