CVSS 3.0
7.5 highCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:HCVE-2016-6581
High (7.5) in python. EPSS 1.9% chance of exploitation in the next 30 days. Fixed in hpack 2.3.0.
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.
Severity
- EPSS
- 1.9% chance of exploitation in the next 30 days; higher than 79% of CVEs (scores of 2026-10-31)
- CWE
- CWE-399
- Published
- Modified
- Record from
- the NVD, synced
Affected
- python:hpack
- python:hyper
Packages (OSV)
| Advisory | Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|---|
| GHSA-ffq8-576r-v26g | PyPI | hpack | >=1.0.0 <2.3.0 | 2.3.0 |
| PYSEC-2017-87 | PyPI | hpack | <2.3.0 | 2.3.0 |