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CVE-2016-6580

priority vulnerable to denial of service

7.5 HighFix available

CVE-2016-6580 is a high vulnerability (CVSS 7.5) in Python Priority Library, published January 10, 2017. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.81%, the 78th percentile. Fixed in priority 1.2.0.

A HTTP/2 implementation built using any version of the Python priority library prior to version 1.2.0 could be targeted by a malicious peer by having that peer assign priority information for every possible HTTP/2 stream ID. The priority tree would happily continue to store the priority information for each stream, and would therefore allocate unbounded amounts of memory. Attempting to actually use a tree like this would also cause extremely high CPU usage to maintain the tree.

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

1.81%Up 0.9 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 priority library prior to version 1.2.0 could be targeted by a malicious peer by having that peer assign priority information for every possible HTTP/2 stream ID. The priority tree would happily continue to store the priority information for each stream, and would therefore allocate unbounded amounts of memory. Attempting to actually use a tree like this would also cause extremely high CPU usage to maintain the tree.

Record
CVE-2016-6580
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
5.0 MediumAV:N/AC:L/Au:N/C:N/I:N/A:P
Weakness
CWE-399
Updated
2026-11-02
CVE List No score

A HTTP/2 implementation built using any version of the Python priority library prior to version 1.2.0 could be targeted by a malicious peer by having that peer assign priority information for every possible HTTP/2 stream ID. The priority tree would happily continue to store the priority information for each stream, and would therefore allocate unbounded amounts of memory. Attempting to actually use a tree like this would also cause extremely high CPU usage to maintain the tree.

Record
CVE-2016-6580
Updated
2026-11-02
EUVDEUVD-2017-0099 No score

A HTTP/2 implementation built using any version of the Python priority library prior to version 1.2.0 could be targeted by a malicious peer by having that peer assign priority information for every possible HTTP/2 stream ID. The priority tree would happily continue to store the priority information for each stream, and would therefore allocate unbounded amounts of memory. Attempting to actually use a tree like this would also cause extremely high CPU usage to maintain the tree.

Record
EUVD-2017-0099
Updated
2026-11-03
GitHub AdvisoriesGHSA-h3q4-6j7f-r24c 6.6

priority vulnerable to denial of service

A HTTP/2 implementation built using any version of the Python priority library prior to version 1.2.0 could be targeted by a malicious peer by having that peer assign priority information for every possible HTTP/2 stream ID. The priority tree would happily continue to store the priority information for each stream, and would therefore allocate unbounded amounts of memory. Attempting to actually use a tree like this would also cause extremely high CPU usage to maintain the tree.

Record
GHSA-h3q4-6j7f-r24c
CVSS 4.0
6.6 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U
CVSS 3.0
7.5 HighCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-770
Updated
2026-11-02
OSV 7.5

A HTTP/2 implementation built using any version of the Python priority library prior to version 1.2.0 could be targeted by a malicious peer by having that peer assign priority information for every possible HTTP/2 stream ID. The priority tree would happily continue to store the priority information for each stream, and would therefore allocate unbounded amounts of memory. Attempting to actually use a tree like this would also cause extremely high CPU usage to maintain the tree.

Record
CVE-2016-6580
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
OSVGHSA-h3q4-6j7f-r24c 6.6

priority vulnerable to denial of service

A HTTP/2 implementation built using any version of the Python priority library prior to version 1.2.0 could be targeted by a malicious peer by having that peer assign priority information for every possible HTTP/2 stream ID. The priority tree would happily continue to store the priority information for each stream, and would therefore allocate unbounded amounts of memory. Attempting to actually use a tree like this would also cause extremely high CPU usage to maintain the tree.

Record
GHSA-h3q4-6j7f-r24c
CVSS 4.0
6.6 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U
CVSS 3.0
7.5 HighCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-770
Updated
2026-11-02
OSVPYSEC-2017-93 No score

A HTTP/2 implementation built using any version of the Python priority library prior to version 1.2.0 could be targeted by a malicious peer by having that peer assign priority information for every possible HTTP/2 stream ID. The priority tree would happily continue to store the priority information for each stream, and would therefore allocate unbounded amounts of memory. Attempting to actually use a tree like this would also cause extremely high CPU usage to maintain the tree.

Record
PYSEC-2017-93
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
priority
PyPI
before 1.2.0
1.2.0
priority
PyPI
before 1.2.0, plus listed versions
0.0.11.0.01.1.01.1.1
1.2.0

History

History
WhenChangedSources
2026-11-03aliasesEUVD
2026-11-02createdCVE List, GitHub Advisories, NVD, OSV

References

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