published October 21, 2026
Uncontrolled recursion in the HTTP/2 HPACK decoder in Apache bRPC before 1.18.0 allows remote attackers to cause denial of service by sending a crafted HTTP/2 header block containing many consecutive Dynamic Table Size Update entries. Each update was decoded by recursively invoking the HPACK decoder, which could exhaust the thread stack before a header field or end of input was reached.
Root Cause:
The bRPC HPACK decoder recursively decoded the next entry after processing a Dynamic Table Size Update. The decoder did not bound the recursion depth, so a long sequence of update entries could consume excessive stack space.
Affected Scenarios:
Use bRPC with the built-in HTTP/2 implementation to accept HTTP/2 traffic from an untrusted network.
How to Fix:
1. Upgrade bRPC to version 1.18.0, which fixes this issue.
2. Apply this patch: https://github.com/apache/brpc/pull/3343
Note:
The fix changes HPACK Dynamic Table Size Update decoding to use iterative parsing instead of recursive parsing.