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CVE-2016-6581

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…

High7.5EPSS 1.9%
Published
Updated
Reserved
Assigned by
mitre

Description

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.

Scores

CVSS scores of CVE-2016-6581, by who scored it
Scored byCVSSScoreVector
NVDNVD · Modified3.0High7.5CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS (exploitation in 30 days)
1.9% · top 21% of all CVEs (3 Nov 2026)

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The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.5.

Weakness

Affected products

  • n/a

    • affected n/a

Affected packages

From reviewed advisories of the GitHub Advisory Database.

References (2)

Sources

The same CVE in the primary databases and aggregators, to check against.

Record last updated .