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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.
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Debian | — | Upgrade python-hpack | Jul 30, 2024 | Jan 10, 2017 |
| Suse | — | Upgrade python3-hpack | Feb 4, 2022 | Jan 10, 2017 |
| Ubuntu | — | No solution exists | Jun 26, 2025 | Jan 10, 2017 |
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