Medium
python-hpack — security advisory
hpack is an HTTP/2 Header Encoding for Python. Prior to version 4.2.0, unbounded variable integer decoding can cause run-away computation on malformed input leading to O(n^2) runtime, effectively blocking further processing with large enough unsanitized input. A fix is available in python-hyper/hpack v4.2.0 to restricted variable integer decoding to uint32 to prevent run-away computation. As a workaround, sanitize input to hpack decoder for long sequences of `0xFF` values to prevent malicious use.
- Products
- python-hpack
- Affected versions
- 1.1.0-1, 2.0.1-1, 2.1.0-1, 3.0.0-1, 3.0.0-2, 3.0.0-3, 3.0.0-4, 4.0.0-2, 4.0.0-3, 4.0.0-4
- Fixed versions
- Not specified
- CVEs
- CVE-2026-59980
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 00:43 UTC · Revision 1
Source evidence
hpack is an HTTP/2 Header Encoding for Python. Prior to version 4.2.0, unbounded variable integer decoding can cause run-away computation on malformed input leading to O(n^2) runtime, effectively blocking further processing with large enough unsanitized input. A fix is available in python-hyper/hpack v4.2.0 to restricted variable integer decoding to uint32 to prevent run-away computation. As a workaround, sanitize input to hpack decoder for long sequences of `0xFF` values to prevent malicious use.
osv:UBUNTU-CVE-2026-59980
python-hpack
Fixed versions: Not specified
python-hpack
Fixed versions: Not specified
python-hpack
Fixed versions: Not specified
python-hpack
Fixed versions: Not specified
python-hpack
Fixed versions: Not specified
python-hpack
Fixed versions: Not specified
python-hpack
Fixed versions: Not specified
Complete source record
{
"id": "3bf96adfad90ef2d84ef9afaa63d6a608e1fc6f90c61361a618258cc28b427fa",
"url": "https://osv.dev/vulnerability/UBUNTU-CVE-2026-59980",
"method": "structured",
"payload": {
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"title": "UBUNTU-CVE-2026-59980",
"summary": "hpack is an HTTP/2 Header Encoding for Python. Prior to version 4.2.0, unbounded variable integer decoding can cause run-away computation on malformed input leading to O(n^2) runtime, effectively blocking further processing with large enough unsanitized input. A fix is available in python-hyper/hpack v4.2.0 to restricted variable integer decoding to uint32 to prevent run-away computation. As a workaround, sanitize input to hpack decoder for long sequences of `0xFF` values to prevent malicious use.",
"evidence": "osv:UBUNTU-CVE-2026-59980",
"products": [
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"evidence": "/affected/0/versions"
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{
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"severity": "medium",
"structured": {
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"aliases": [
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"metrics": [
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"type": "CVSS_V4",
"score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N"
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{
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"affected": [
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"ecosystem": "Ubuntu:16.04:LTS"
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"2.0.1-1",
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"database_specific": {
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"ecosystem_specific": {
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"ecosystem": "Ubuntu:20.04:LTS"
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"versions": [
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"versions": [
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"ecosystem": "Ubuntu:26.04:LTS"
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"versions": [
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"database_specific": {
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],
"modified": "2026-10-17T12:56:00.350186752Z",
"provider": "osv",
"upstream": [
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],
"references": [
"https://ubuntu.com/security/CVE-2026-59980",
"https://www.cve.org/CVERecord?id=CVE-2026-59980",
"https://github.com/python-hyper/hpack/security/advisories/GHSA-8v8h-hg4w-mvq2",
"https://github.com/python-hyper/hpack/commit/8cfb02c547740e16dbfe7aba77bad84b297cec2c",
"https://cs.opensource.google/go/x/net/+/master:http2/hpack/hpack.go;l=468;drc=8e2b117aee74f6b86c207a808b0255de45c0a18a",
"https://docs.rs/http2/0.5.19/src/http2/hpack/decoder.rs.html#403"
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"evidence": "/upstream"
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"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 354522,
"published_at": "2026-09-23T23:17:00+00:00"
}