Is CVE-2026-34520 in the CISA KEV catalog?

No. CVE-2026-34520 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-34520?

CVE-2026-34520 has a CVSS v3 base score of 9.1 (CRITICAL).

What is the EPSS score for CVE-2026-34520?

CVE-2026-34520 has an EPSS score of 0.46% (37th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-34520?

Upgrade python-aiohttp on debian 11 to 3.7.4-1+deb11u2 or later.

CVE & CISA-KEV Catalog

CVE-2026-34520

CRITICAL

9.1

CVSS v3

NVD

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.

CWE-113

How to fix

Remediation Available

python-aiohttpDebian

Fixed in:3.7.4-1+deb11u2CVE-2026-34520

Fixed in:3.13.5-1CVE-2026-34520

TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityHigh

AvailabilityHigh

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Exploit Intelligence

0.46%probability of exploitation in 30 days

37thpercentile

Low risk: more likely to be exploited than 37% of all known CVEs.

References

Patch2

Release Notes1

github.com

Related Vulnerabilities

Other CWE-113 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2022-37436	Medium	5.3	58%	-	Fix
CVE-2024-52875	High	8.8	29%	-	-
CVE-2016-5699	Medium	6.1	10%	-	Fix
CVE-2016-8024	High	8.1	8.7%	-	-
CVE-2017-17742	Medium	5.3	5.8%	-	Fix
CVE-2016-5325	Medium	6.1	4.1%	-	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-04-16.