CVE-2026-61916: Apache bRPC: Out-of-bounds Read in URL and Header Lookup Tables on Unsigned-char Platforms

Out-of-bounds reads in URL parsing and case-insensitive header lookup in Apache bRPC before version 1.18.0 on platforms where plain char is unsigned, such as ARM64, allow remote attackers to cause a process crash and denial of service by sending crafted input containing bytes with the high bit set.

Root Cause: Two 256-entry lookup tables are accessed through pointers biased by 128 so that valid indices are in the range -128 to 127. Input bytes are promoted from plain char to int without first normalizing them to the signed-char range. On affected platforms, bytes in the range 0x80 to 0xFF therefore become indices 128 to 255 and read up to 127 bytes beyond the end of the underlying tables.

Affected Scenarios: A remotely accessible bRPC HTTP server on an affected platform can reach the vulnerable URL lookup through an unauthenticated request URI containing a high-bit byte. The case-insensitive lookup is also reachable when untrusted header names are processed through APIs such as the HTTP/2 HPACK path. HTTP/1 header names containing high-bit bytes are rejected by the HTTP/1 parser before reaching the vulnerable lookup. Builds where plain char is signed, which commonly include x8664 builds, are not affected by this issue.

How to Fix: Choose one of the following options: 1. Upgrade Apache bRPC to version 1.18.0 or later. 2. Apply the patch from https://github.com/apache/brpc/pull/3376 .

The fix normalizes lookup-table indices to the signed-char range before accessing the biased tables.