Vulnerability Report

CVE-2016-6581

Title: Python Hpack Denial of Service (DoS)

DoS

Proof Of Concept

No public PoC currently indexed for CVE-2016-6581.

CWE Category CWE-399
Published Date Jan 10, 2017
Modified Date Jun 17, 2026
Exploit Status Not Found
Score 7.5 CVSS v3.0
Exploit Probability (EPSS)
1.76%

Vulnerability Summary

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 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.

Impacted Vendors

P
python 2
V
vercel 1

Reference Links

http://www.securityfocus.com/bid/92315 https://python-hyper.org/hpack/en/latest/security/CVE-2016-6581.html http://www.securityfocus.com/bid/92315 https://python-hyper.org/hpack/en/latest/security/CVE-2016-6581.html
CVSS v3.0
Source Entity [email protected]
Severity HIGH
7.5
Attack Vector
NETWORK
Complexity
LOW
Privileges
N/A
Interaction
NONE
Confidentiality
N/A
Integrity
N/A
Availability
N/A
Scope
UNCHANGED
RAW VECTOR CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS v2.0
Source Entity [email protected]
Severity HIGH
7.8
Access Vector
N/A
Authentication
N/A
RAW VECTOR AV:N/AC:L/Au:N/C:N/I:N/A:C

Associated Attack Patterns (CAPEC)

Total: Patterns

CVE-2016-6581 Exploits & PoCs (Proof Of Concept)

No public PoCs found in our database for this CVE.

MODIFIED

Vulnerability data updated via NVD.

MODIFIED

Vulnerability data updated via NVD.

MODIFIED

Vulnerability data or affected products updated.

PUBLISHED

Vulnerability first announced in NVD.

Attack Vector Matrix

Access Vector NETWORK
Complexity LOW
Privileges N/A
Interaction NONE
CVSS Vector String CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected Stack

No specific products linked.