InsomniaX 2.1.8 Arbitrary Kernel Extension Loading

It was found that the loader application bundled with InsomniaX can be used to load arbitrary Kernel Extensions (kext). The loader is normally used to load a kext file that is needed to disable the Lid Sleep. A flaw has been found in the loader that allows a local attacker to load (or unload) any arbitrary kext file. Version 2.1.8 is affected.


MD5 | 703ccd1c6eecfd818433456c702fa221

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InsomniaX loader allows loading of arbitrary Kernel Extensions
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Yorick Koster, April 2017

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Abstract
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It was found that the loader application bundled with InsomniaX can be
used to load arbitrary Kernel Extensions (kext). The loader is normally
used to load a kext file that is needed to disable the Lid Sleep. A flaw
has been found in the loader that allows a local attacker to load (or
unload) any arbitrary kext file.

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See also
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- http://semaja2.net/2017/06/insomniax-security-notice/
- http://semaja2.net/2017/06/thank-you-and-farewell-for-now/

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Tested versions
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This issue was successfully verified on InsomniaX version 2.1.8.

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Fix
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There is currently no fix available. The author of InsomniaX reports
that InsomniaX is no longer supported. As a workaround, remove the
setuid bit from the loader file. Doing so will prevent users from
disabling the Lid Sleep.

sudo chmod u-s /Applications/InsomniaX.app/Contents/Resources/loader

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Details
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https://www.securify.nl/advisory/SFY20170405/insomniax-loader-allows-loading-of-arbitrary-kernel-extensions.html

This issue exists because InsomniaX tries to load the kext file form the user's home folder. When started the loader first changes the owner of the kext file to user root and group wheel. This is required or else the kext loader will refuse to load the kext. After changing the owner, loader will call kextload with the path set to the kext located in the user's home directory. Replacing InsomniaX' kext with a different one will cause the loader to load this kext instead.

struct passwd *pw = getpwuid(getuid());

char *homedir = pw->pw_dir;

char *supportPath = strcat(homedir, "/Library/Application Support/InsomniaX");
const char *kextPath = strcat(supportPath, "/Insomnia_r11.kext");

switch(myCommand->authorizedCommandId)
{
case kMyAuthorizedLoad: {
/* Child code. */
if(fork() == 0) {
#ifdef DEBUG
fprintf(stderr, "CHOWN\n");
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