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
Published Jan 10, 2017
8.7
HIGHCVSS 4.0
EPSS 1.83%
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.
Affected products
No data.
No data.
No Red Hat product state for this CVE.
No package ranges for this CVE.
Remediation
No remediation recorded yet.
Metrics
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
AV:N/AC:L/Au:N/C:N/I:N/A:C
This CVE is not in the KEV list.
No CISA SSVC assessment for this CVE yet.
Estimated probability of exploitation in the wild in the next 30 days (FIRST EPSS). As of Oct 1, 2026.
Score over time
2022–2026- EPSS v2
- EPSS v3
- EPSS v4
- EPSS v5
Percentile over time
- EPSS v2
- EPSS v3
- EPSS v4
- EPSS v5
Table of values (10 key points)
Flat stretches are collapsed; showing up to 120 newest points.
| Date | Score | Percentile | Model |
|---|---|---|---|
| Oct 1, 2026 | 1.83% (0.01826) | 78.03th | v5 (v2026.06.15) |
| Jun 15, 2026 | 1.76% (0.01757) | 74.96th | v5 (v2026.06.15) |
| Mar 17, 2025 | 0.37% (0.00373) | 56.89th | v4 (v2025.03.14) |
| Dec 12, 2024 | 0.10% (0.00096) | 42.02th | v3 (v2023.03.01) |
| Jul 10, 2024 | 0.10% (0.00096) | 40.75th | v3 (v2023.03.01) |
| Mar 7, 2023 | 0.10% (0.00096) | 38.73th | v3 (v2023.03.01) |
| Mar 6, 2023 | 0.89% (0.00885) | 27.89th | v2 (v2022.01.01) |
| Sep 10, 2022 | 0.89% (0.00885) | 26.24th | v2 (v2022.01.01) |
| Apr 1, 2022 | 0.89% (0.00885) | 24.24th | v2 (v2022.01.01) |
| Feb 4, 2022 | 0.89% (0.00885) | 10.50th | v2 (v2022.01.01) |
References (7)
- http://python-hyper.org/projects/hpack/en/stable/security/CVE-2016-6581.html
- http://www.securityfocus.com/bid/92315 vdb-entryx_refsource_BIDThird Party AdvisoryVDB Entry
- https://github.com/advisories/GHSA-ffq8-576r-v26g Advisory
- https://github.com/pypa/advisory-database/tree/main/vulns/hpack/PYSEC-2017-87.yaml
- https://nvd.nist.gov/vuln/detail/CVE-2016-6581
- https://python-hyper.org/hpack/en/latest/security/CVE-2016-6581.html x_refsource_CONFIRMMitigationVendor Advisory
- https://web.archive.org/web/20200227233559/http://www.securityfocus.com/bid/92315
| Link | Providers | Tags |
|---|---|---|
| http://python-hyper.org/projects/hpack/en/stable/security/CVE-2016-6581.html | ||
| http://www.securityfocus.com/bid/92315 | vdb-entryx_refsource_BIDThird Party AdvisoryVDB Entry | |
| https://github.com/advisories/GHSA-ffq8-576r-v26g | Advisory | |
| https://github.com/pypa/advisory-database/tree/main/vulns/hpack/PYSEC-2017-87.yaml | ||
| https://nvd.nist.gov/vuln/detail/CVE-2016-6581 | ||
| https://python-hyper.org/hpack/en/latest/security/CVE-2016-6581.html | x_refsource_CONFIRMMitigationVendor Advisory | |
| https://web.archive.org/web/20200227233559/http://www.securityfocus.com/bid/92315 |
Change history (0)
No recorded changes yet.