CVE-2016-6581
HPACK Denial of Service vulnerability (HPACK Bomb)
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.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- None
What an attacker can affect
- Confidentiality
- None
- Integrity
- None
- Availability
- High
Exploit likelihood
What each source reports
NVD Score used
7.5
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.
- Record
CVE-2016-6581- CVSS 3.0
- 7.5 High
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - CVSS 2.0
- 7.8 High
AV:N/AC:L/Au:N/C:N/I:N/A:C - Weakness
- CWE-399
- Updated
- 2026-11-02
CVE List No score
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.
- Record
CVE-2016-6581- Updated
- 2026-11-02
EUVDEUVD-2017-0059 No score
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.
- Record
EUVD-2017-0059- Updated
- 2026-11-03
GitHub AdvisoriesGHSA-ffq8-576r-v26g
8.7
HPACK Denial of Service vulnerability (HPACK Bomb)
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.
- Record
GHSA-ffq8-576r-v26g- CVSS 4.0
- 8.7 High
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
- 7.5 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - Updated
- 2026-11-02
OSV
7.5
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.
- Record
CVE-2016-6581- CVSS 3.0
- 7.5 High
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - Updated
- 2026-11-02
OSVDEBIAN-CVE-2016-6581
7.5
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.
- Record
DEBIAN-CVE-2016-6581- CVSS 3.0
- 7.5 High
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - Updated
- 2026-11-02
Show 6 moreShow less
OSVGHSA-ffq8-576r-v26g
8.7
HPACK Denial of Service vulnerability (HPACK Bomb)
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.
- Record
GHSA-ffq8-576r-v26g- CVSS 4.0
- 8.7 High
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
- 7.5 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - Updated
- 2026-11-02
OSVUBUNTU-CVE-2016-6581
7.5
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.
- Record
UBUNTU-CVE-2016-6581- CVSS 3.0
- 7.5 High
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - Updated
- 2026-11-02
OSVopenSUSE-SU-2024:11230-1 No score
python36-hpack-4.0.0-1.6 on GA media
These are all security issues fixed in the python36-hpack-4.0.0-1.6 package on the GA media of openSUSE Tumbleweed.
- Record
openSUSE-SU-2024:11230-1- Updated
- 2026-11-02
OSVopenSUSE-SU-2024:14140-1 No score
python310-hpack-4.0.0-2.7 on GA media
These are all security issues fixed in the python310-hpack-4.0.0-2.7 package on the GA media of openSUSE Tumbleweed.
- Record
openSUSE-SU-2024:14140-1- Updated
- 2026-11-02
OSVopenSUSE-SU-2026:11556-1 No score
python313-hpack-4.2.0-1.1 on GA media
These are all security issues fixed in the python313-hpack-4.2.0-1.1 package on the GA media of openSUSE Tumbleweed.
- Record
openSUSE-SU-2026:11556-1- Updated
- 2026-11-02
OSVPYSEC-2017-87 No score
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.
- Record
PYSEC-2017-87- Updated
- 2026-11-02
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
hpackPyPI |
1.0.0 up to 2.3.0 | 2.3.0 |
python-hpackDebian:12 |
before 2.3.0-1 | 2.3.0-1 |
python-hpackDebian:13 |
before 2.3.0-1 | 2.3.0-1 |
python-hpackDebian:14 |
before 2.3.0-1 | 2.3.0-1 |
hpackPyPI |
1.0.0 up to 2.3.0, plus listed versions 1.0.11.1.02.0.02.0.12.1.02.1.12.2.0 |
2.3.0 |
hpackPyPI |
before 2.3.0, plus listed versions 1.0.01.0.11.1.02.0.02.0.12.1.02.1.12.2.0 |
2.3.0 |
python-hpackUbuntu:16.04:LTS |
All versions, plus listed versions 1.1.0-12.0.1-12.1.0-1 |
None known |
python-hpackopenSUSE:Tumbleweed |
before 4.0.0-2.7 | 4.0.0-2.7 |
python-hpackopenSUSE:Tumbleweed |
before 4.2.0-1.1 | 4.2.0-1.1 |
History
| Recorded | Changed | Sources |
|---|---|---|
| aliases | EUVD | |
| first indexed | CVE List, GitHub Advisories, NVD, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2016-6581 is a high vulnerability (CVSS 7.5) in Python Hpack, published January 10, 2017. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.88%, the 79th percentile. Fixed in hpack 2.3.0.
References
securityfocus.com/bid/92315
python-hyper.org/hpack/en/latest/security/CVE-2016-6581.html
nvd.nist.gov/vuln/detail/CVE-2016-6581
github.com/advisories/GHSA-ffq8-576r-v26g
python-hyper.org/projects/hpack/en/stable/security/CVE-2016-6581.html
github.com/pypa/advisory-database/tree/main/vulns/hpack/PYSEC-2017-87.yaml
Show 9 moreShow less
web.archive.org/web/20200227233559/http://www.securityfocus.com/bid/92315
security-tracker.debian.org/tracker/CVE-2016-6581
github.com/python-hyper/hpack
ubuntu.com/security/CVE-2016-6581
github.com/python-hyper/hpack/pull/56
openwall.com/lists/oss-security/2016/08/04/3
cve.org/CVERecord?id=CVE-2016-6581
suse.com/security/cve/CVE-2016-6581
suse.com/security/cve/CVE-2026-59980