CVE-2026-59980: CWE-400: Uncontrolled Resource Consumption in python-hyper hpack
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.
AI Analysis
Technical Summary
The python-hyper hpack library versions before 4.2.0 contain a CWE-400 uncontrolled resource consumption vulnerability. Specifically, the unbounded variable integer decoding can lead to O(n^2) runtime complexity on malformed input, causing run-away computation and denial of service. The vulnerability is addressed in version 4.2.0 by limiting variable integer decoding to 32-bit unsigned integers. Input sanitization to prevent long sequences of 0xFF bytes can serve as a temporary mitigation.
Potential Impact
An attacker can supply specially crafted malformed input to the hpack decoder causing excessive CPU consumption due to quadratic runtime complexity. This can lead to denial of service by blocking further processing in applications using vulnerable versions of the hpack library. There is no indication of privilege escalation or data compromise from this vulnerability.
Mitigation Recommendations
A fix is available in python-hyper/hpack version 4.2.0 which restricts variable integer decoding to uint32, preventing run-away computation. Users should upgrade to version 4.2.0 or later. As a temporary workaround, sanitize inputs to the hpack decoder to prevent long sequences of 0xFF bytes that could trigger the vulnerability.
CVE-2026-59980: CWE-400: Uncontrolled Resource Consumption in python-hyper hpack
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.
CVSS v4.0
Score 6.3medium
Affected software
python-hyper
hpack
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The python-hyper hpack library versions before 4.2.0 contain a CWE-400 uncontrolled resource consumption vulnerability. Specifically, the unbounded variable integer decoding can lead to O(n^2) runtime complexity on malformed input, causing run-away computation and denial of service. The vulnerability is addressed in version 4.2.0 by limiting variable integer decoding to 32-bit unsigned integers. Input sanitization to prevent long sequences of 0xFF bytes can serve as a temporary mitigation.
Potential Impact
An attacker can supply specially crafted malformed input to the hpack decoder causing excessive CPU consumption due to quadratic runtime complexity. This can lead to denial of service by blocking further processing in applications using vulnerable versions of the hpack library. There is no indication of privilege escalation or data compromise from this vulnerability.
Mitigation Recommendations
A fix is available in python-hyper/hpack version 4.2.0 which restricts variable integer decoding to uint32, preventing run-away computation. Users should upgrade to version 4.2.0 or later. As a temporary workaround, sanitize inputs to the hpack decoder to prevent long sequences of 0xFF bytes that could trigger the vulnerability.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-07-07T19:41:00.004Z
- Cvss Version
- 4.0
- State
- PUBLISHED
Threat ID: 6ab453a8f7a7c541066aa604
Added to database: 09/23/2026, 22:33:12 UTC
Last enriched: 09/23/2026, 22:47:56 UTC
Last updated: 09/24/2026, 02:07:27 UTC
Views: 9
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