HPACK Bomb Denial of Service in Python HPACK
CVE-2016-6581 is a denial-of-service vulnerability affecting HTTP/2 implementations built with Python HPACK library versions 1.0.0 through 2.2.0. The issue arises from HPACK dynamic table handling: an attacker can insert a header field sized to exactly fill the HPACK dynamic header table, then send header blocks composed of repeated indexed references that expand that entry repeatedly during decompression. This creates an extreme compression-amplification condition, described as an "HPACK Bomb," where a relatively small compressed input can decompress into a very large in-memory representation on the target. The provided description states that as little as 16 kB of attacker-controlled data can expand to roughly 64 MB on the receiving system.
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Impact, mitigation & remediation
What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
Impact
What an attacker gets, and what they’ve been doing with it.
Mitigation
If you can’t patch tonight, do this now.
Remediation
Patch, then assume compromise.
Exploits
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Affected products & vendors
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
Recent activity
6 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
An HTTP/2 denial-of-service weakness involving HPACK header compression abuse, where small messages decompress into very large memory-consuming structures on the server.
A denial-of-service technique abusing HTTP/2 HPACK header compression to force excessive memory allocation and crash a server.
A previously disclosed HPACK-related denial-of-service issue referenced as an inspiration for HTTP/2 Bomb.
A prior HPACK Bomb vulnerability related to HTTP/2 header compression amplification.
The version that knows your environment.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.