CVE-2026-59980
Medium
Description
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.
SeverityMedium
CVSS6.3
Exploit probability—
ProductHpack
PublishedSep 23, 2026
First seenSep 23, 2026
Weakness typeCWE-400Uncontrolled resource consumption
How to fix
Update
- hpack4.2.0 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| hpackPyPI | v < 4.2.0 | 4.2.0 |
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