CVE-2016-6581
HIGHEPSS 75th pctlDescription
A HTTP/2 implementation built using any version of the Python HPACK library between v1.0.0 and v2.2.0 could be targeted for a denial of service attack, specifically a so-called "HPACK Bomb" attack. This attack occurs when an attacker inserts a header field that is exactly the size of the HPACK dynamic header table into the dynamic header table. The attacker can then send a header block that is simply repeated requests to expand that field in the dynamic table. This can lead to a gigantic compression ratio of 4,096 or better, meaning that 16kB of data can decompress to 64MB of data on the target machine.
How to fix
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Exploit Intelligence
Elevated risk: more likely to be exploited than 75% of all known CVEs.
References
Related Vulnerabilities
Other CWE-399 (Resource Management Errors) vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2009-3103 | High | 10.0 | 90% | - | - |
| CVE-2009-0075 | High | 9.3 | 85% | - | - |
| CVE-2005-1790 | Low | 2.6 | 83% | - | - |
| CVE-2010-0806 | High | 8.8 | 82% | KEV | - |
| CVE-2009-2526 | High | 7.8 | 82% | - | - |
| CVE-2015-1868 | High | 7.8 | 82% | - | Fix |
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Start freeThis product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-05-06.