Low
AIOHTTP: C parser (llhttp) accepts null bytes and control characters in response header values - header injection / security bypass
Type: advisorySources: OSV
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.
- Products
- Not specified
- Affected versions
- Not specified
- Fixed versions
- Not specified
- CVEs
- CVE-2026-34520
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 7 Nov 2026, 12:04 UTC · Revision 1
Source evidence
AIOHTTP: C parser (llhttp) accepts null bytes and control characters in response header values - header injection / security bypass
core-osv · Original sourcePublished 1 Apr 2026, 20:27 UTC
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.
osv:CVE-2026-34520
Complete source record
{
"id": "48b474337a86ec188e64340340bdb542287de42e21b68e89b3994a20b73a3977",
"url": "https://osv.dev/vulnerability/CVE-2026-34520",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "AIOHTTP: C parser (llhttp) accepts null bytes and control characters in response header values - header injection / security bypass",
"summary": "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.",
"evidence": "osv:CVE-2026-34520",
"products": [],
"severity": "low",
"structured": {
"id": "CVE-2026-34520",
"aliases": [
"CVE-2026-34520",
"GHSA-63hf-3vf5-4wqf",
"PYSEC-2026-2102"
],
"metrics": [
{
"type": "CVSS_V4",
"score": "CVSS: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"
}
],
"affected": [
{
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"type": "GIT",
"events": [
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},
{
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{
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}
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"database_specific": {
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"cpe": "cpe:2.3:a:aiohttp:aiohttp:*:*:*:*:*:*:*:*",
"range": [
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"source": "CPE_RANGE"
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"source": "REFERENCES_COMMIT"
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"database_specific": {
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}
}
],
"modified": "2026-10-28T02:30:50.736667814Z",
"provider": "osv",
"references": [
"https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4",
"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/34xxx/CVE-2026-34520.json",
"https://github.com/aio-libs/aiohttp/security/advisories/GHSA-63hf-3vf5-4wqf",
"https://nvd.nist.gov/vuln/detail/CVE-2026-34520",
"https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4"
],
"provider_metadata": {
"cwe_ids": [
"CWE-113"
],
"cna_assigner": "GitHub_M",
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/34xxx/CVE-2026-34520.json"
}
},
"related_cves": [
{
"value": "CVE-2026-34520",
"evidence": "/id"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 519226,
"published_at": "2026-04-01T20:27:48.35+00:00"
}