CVE-2026-34520

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 Metrics

• v4.0•LOW•Score: 2.7CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U
• v4.0•LOW•Score: 2.7CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/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
• v3.1•CRITICAL•Score: 9.1CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

EPSS Trends

Current EPSS score: 0.46%• Percentile: 39%

Techniques & Countermeasures

• CWE-113•Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')

  The product receives data from an HTTP agent/component (e.g., web server, proxy, browser, etc.), but it does not neutralize or incorrectly neutralizes CR and LF characters before the data is included in outgoing HTTP headers.

Affected Systems

• aio-libs•aiohttp

  < 3.13.4

• aiohttp•aiohttp

  < 3.13.4

• chainguard•airflow-2

  < 2.11.2-r5

• chainguard•airflow-3

  < 3.2.1-r0 | < 3.1.8-r11

• chainguard•airflow-core-2

  < 2.11.2-r3

• chainguard•authentik-2025.12

  < 2025.12.4-r3

• chainguard•authentik-2026.2

  < 2026.2.1-r3

• chainguard•authentik-fips-2025.12

  < 2025.12.4-r3

• chainguard•authentik-fips-2026.2

  < 2026.2.1-r3

• chainguard•awx

  < 24.6.1-r33

• chainguard•checkov

  < 3.2.517-r0

• chainguard•dask-kubernetes

  < 2026.3.0-r3

• chainguard•datahub-ingestion

  < 1.6.0-r1

• chainguard•datahub-ingestion-fips

  < 1.5.0.1-r1

• chainguard•keep-api

  < 0.51.0-r2

• chainguard•keep-api-fips

  < 0.51.0-r2

• chainguard•kserve-storage-controller

  < 0.17.0-r2

• chainguard•kubeflow-pipelines-visualization-server

  < 2.16.0-r4

• chainguard•litellm

  < 1.82.3.0-r3

• chainguard•metaflow-service

  < 2.5.0-r10

• chainguard•metaflow-service-fips

  < 2.5.0-r2

• chainguard•open-webui

  < 0.8.12-r3

• chainguard•py3-cassandra-medusa

  < 0.27.1-r2

• chainguard•py3.13-scanner-test-libraries-aiohttp

  < 0.0.1-r3

• chainguard•request-1276

  < 0.27.1-r2

• chainguard•text-generation-inference

  < 3.3.7-r10

• chainguard•tritonserver-backend-vllm-cuda-12.9

  < 25.9.0_git20260318-r1

• chainguard•tritonserver-backend-vllm-cuda-13.0

  < 25.11-r3

• wolfi•airflow-3

  < 3.2.1-r0 | < 3.1.8-r11

• wolfi•checkov

  < 3.2.517-r0

• wolfi•dask-kubernetes

  < 2026.3.0-r3

• wolfi•kserve-storage-controller

  < 0.17.0-r2

• wolfi•kubeflow-pipelines-visualization-server

  < 2.16.0-r4

• wolfi•open-webui

  < 0.8.12-r3

• wolfi•py3-cassandra-medusa

  < 0.27.1-r2

• debian•python-aiohttp

  < 3.7.4-1+deb11u2 | all | all | < 3.13.5-1

• ubuntu•python-aiohttp

  all | all

• PyPI•aiohttp

  < 3.13.4

References (10)

• https://github.com/aio-libs/aiohttp/security/advisories/GHSA-63hf-3vf5-4wqf
• https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4
• https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4
• https://nvd.nist.gov/vuln/detail/CVE-2026-34520
• https://github.com/aio-libs/aiohttp
• https://github.com/pypa/advisory-database/tree/main/vulns/aiohttp/PYSEC-2026-2102.yaml
• https://ubuntu.com/security/CVE-2026-34520
• https://www.cve.org/CVERecord?id=CVE-2026-34520
• https://security-tracker.debian.org/tracker/CVE-2026-34520
• https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/34xxx/CVE-2026-34520.json