Every CVE Search/ Get API key

CVE-2016-6581

HPACK Denial of Service vulnerability (HPACK Bomb)

7.5 HighFix available

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

1.88%Up 1.0 points since Feb 4, 2022
90%50%10%1%

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 HighCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS 2.0
7.8 HighAV: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 HighCVSS: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 HighCVSS: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 HighCVSS: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 HighCVSS: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 HighCVSS: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 HighCVSS: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 HighCVSS: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

Affected packages
PackageAffectedFixed
hpack
PyPI
1.0.0 up to 2.3.0
2.3.0
python-hpack
Debian:12
before 2.3.0-1
2.3.0-1
python-hpack
Debian:13
before 2.3.0-1
2.3.0-1
python-hpack
Debian:14
before 2.3.0-1
2.3.0-1
hpack
PyPI
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
hpack
PyPI
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-hpack
Ubuntu:16.04:LTS
All versions, plus listed versions
1.1.0-12.0.1-12.1.0-1
None known
python-hpack
openSUSE:Tumbleweed
before 4.0.0-2.7
4.0.0-2.7
python-hpack
openSUSE:Tumbleweed
before 4.2.0-1.1
4.2.0-1.1

History

History
RecordedChangedSources
aliasesEUVD
first indexedCVE 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

Show 9 moreShow less
MoveEnter Open