CVE-2016-6581
Summary
| CVE | CVE-2016-6581 |
|---|---|
| State | PUBLISHED |
| Assigner | mitre |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2017-01-10 15:59:00 UTC |
| Updated | 2026-05-06 22:30:45 UTC |
| 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. |
Risk And Classification
Primary CVSS: v3.0 7.5 HIGH from [email protected]
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS: 0.003730000 probability, percentile 0.590300000 (date 2026-05-11)
Problem Types: CWE-399 | n/a
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.0 | [email protected] | Primary | 7.5 | HIGH | CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
| 2.0 | [email protected] | Primary | 7.8 | AV:N/AC:L/Au:N/C:N/I:N/A:C |
CVSS v3.0 Breakdown
Attack Vector
NetworkAttack Complexity
LowPrivileges Required
NoneUser Interaction
NoneScope
UnchangedConfidentiality
NoneIntegrity
NoneAvailability
HighCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS v2.0 Breakdown
Access Vector
NetworkAccess Complexity
LowAuthentication
NoneConfidentiality
NoneIntegrity
NoneAvailability
CompleteAV:N/AC:L/Au:N/C:N/I:N/A:C
NVD Known Affected Configurations (CPE 2.3)
| Type | Vendor | Product | Version | Update | Edition | Language |
|---|---|---|---|---|---|---|
| Application | Python | Hpack | 1.0 | All | All | All |
| Application | Python | Hpack | 2.0 | All | All | All |
| Application | Python | Hpack | 2.0.1 | All | All | All |
| Application | Python | Hpack | 2.1.1 | All | All | All |
| Application | Python | Hpack | 2.2 | All | All | All |
| Application | Python | Hyper | 0.4 | All | All | All |
| Application | Python | Hyper | 0.6 | All | All | All |
Vendor Declared Affected Products
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| Maze Found | Read the Docs | af854a3a-2127-422b-91ae-364da2661108 | python-hyper.org | Mitigation, Vendor Advisory |
| Python HPACK CVE-2016-6581 Remote Denial of Service Vulnerability | af854a3a-2127-422b-91ae-364da2661108 | www.securityfocus.com | Third Party Advisory, VDB Entry |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
No vendor comments have been submitted for this CVE.
Legacy QID Mappings
- 981106 Python (pip) Security Update for hpack (GHSA-ffq8-576r-v26g)