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.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||
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| python-hyper | hpack | affected |
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History
Wed, 23 Sep 2026 22:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| 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. | |
| Title | hpack: Unbounded variable integer decoding can cause run-away computation on malformed input | |
| Weaknesses | CWE-400 | |
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cvssV4_0
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MITRE
Status: PUBLISHED
Assigner: GitHub_M
Published:
Updated: 2026-09-23T22:07:35.095Z
Reserved: 2026-07-07T19:41:00.004Z
Link: CVE-2026-59980
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