On Tue, Apr 07, 2026 at 09:48:07AM +0200, Greg Kroah-Hartman wrote:
> Subject: [PATCH 02/10] BUG: hlua: fix stack overflow in httpclient headers
> conversion
> hlua_httpclient_table_to_hdrs() declares a VLA of size
> global.tune.max_http_hdr (default 101) on the stack but never checks
> hdr_num against that bound. A Lua script that supplies a header table
> with more than 101 values writes struct http_hdr entries (two ist =
> two heap pointers + two lengths) past the end of the VLA, smashing
> the stack frame.
>
> Trigger from any Lua action/task/service:
>
> local hc = core.httpclient()
> local v = {}
> for i = 1, 300 do v[i] = "x" end
> hc:get{ url = "http://127.0.0.1/";, headers = { ["X"] = v } }
>
> Each out-of-bounds entry writes a heap pointer (controllable
> allocation contents via istdup) plus an attacker-chosen length onto
> the stack, overwriting the saved return address. With no stack
> canary, this is direct RCE; with a canary, it requires a leak first.
>
> Reachable from any deployment that loads Lua scripts. While Lua
> scripts are nominally trusted, this turns "can edit Lua" into "can
> execute arbitrary native code", which is a meaningful boundary in
> many setups (Lua sandbox escape).
>
> This must be backported as far as the httpclient Lua API exists.
Merged as a BUG/MINOR. I removed the paragraph about executing arbitrary code
and the part about an RCE. It's a bit excessive since it requires an access to
the lua script, which already allows to execute anything.
Thanks!
--
William Lallemand
