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7203664474
CheckKeyTypes validates incoming key type definitions from XkbSetMap
requests but does not enforce an upper bound on numLevels. A client can set
numLevels up to 255 on a non-canonical key type, which is stored in the
server's type table.
When ChangeKeyboardMapping later triggers XkbUpdateKeyTypesFromCore, the
function XkbKeyTypesForCoreSymbols computes groupsWidth from num_levels and
uses the XKB_OFFSET(g, l) = (g * groupsWidth) + l macro to index into
tsyms[], a stack-allocated buffer of XkbMaxSymsPerKey (252) entries. With
num_levels=255, groupsWidth=255, and indices reach up to 3*255+254 = 1019,
overflowing the 252-element stack buffer by 767 KeySym-sized entries.
Fix by rejecting numLevels values greater than XkbMaxShiftLevel (63) in
CheckKeyTypes, alongside the existing lower-bound check for numLevels < 1.
This vulnerability was discovered by:
Anonymous working with TrendAI Zero Day Initiative
ZDI-CAN-30160
Assisted-by: Claude:claude-opus-4-6
(cherry picked from commit
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|---|---|---|
| .. | ||
| ddxBeep.c | ||
| ddxCtrls.c | ||
| ddxKillSrv.c | ||
| ddxLEDs.c | ||
| ddxLoad.c | ||
| ddxPrivate.c | ||
| ddxVT.c | ||
| maprules.c | ||
| meson.build | ||
| README.compiled | ||
| xkb-procs.h | ||
| xkb.c | ||
| xkbAccessX.c | ||
| xkbActions.c | ||
| XKBAlloc.c | ||
| xkbDflts.h | ||
| xkbEvents.c | ||
| xkbfmisc.c | ||
| XKBGAlloc.c | ||
| xkbgeom.h | ||
| xkbInit.c | ||
| xkbLEDs.c | ||
| XKBMAlloc.c | ||
| XKBMisc.c | ||
| xkbout.c | ||
| xkbPrKeyEv.c | ||
| xkbSwap.c | ||
| xkbtext.c | ||
| xkbUtils.c | ||
| XKM_file_format.txt | ||
| xkmread.c | ||
The X server uses this directory to store the compiled version of the
current keymap and/or any scratch keymaps used by clients. The X server
or some other tool might destroy or replace the files in this directory,
so it is not a safe place to store compiled keymaps for long periods of
time. The default keymap for any server is usually stored in:
X<num>-default.xkm
where <num> is the display number of the server in question, which makes
it possible for several servers *on the same host* to share the same
directory.
Unless the X server is modified, sharing this directory between servers on
different hosts could cause problems.