CVE-2021-31166 - Proof Of Concept For CVE-2021-31166, A Remote HTTP.sys Use-After-Free Triggered Remotely
This is a proof of concept for CVE-2021-31166 ("HTTP Protocol Stack Remote Code Execution Vulnerability"), a use-after-free dereference in http.sys patched by Microsoft in May 2021. According to this tweet the vulnerability has been found by @_mxms and @fzzyhd1.
The bug itself happens in http!UlpParseContentCoding where the function has a local LIST_ENTRY and appends item to it. When it's done, it moves it into the Request structure; but it doesn't NULL out the local list. The issue with that is that an attacker can trigger a code-path that frees every entries of the local list leaving them dangling in the Request object.
Here is the bugcheck:
Analysis * * * ******************************************************************************* KERNEL_SECURITY_CHECK_FAILURE (139) A kernel component has corrupted a critical data structure. The corruption could potentially allow a malicious user to gain control of this machine. Arguments: Arg1: 0000000000000003, A LIST_ENTRY has been corrupted (i.e. double remove). Arg2: fffff90ea867ee40, Address of the trap frame for the exception that caused the BugCheck Arg3: fffff90ea867ed98, Address of the exception record for the exception that caused the BugCheck Arg4: 0000000000000000, Reserved ">
KDTARGET: Refreshing KD connection
*** Fatal System Error: 0x00000139
(0x0000000000000003,0xFFFFF90EA867EE40,0xFFFFF90EA867ED98,0x0000000000000000)
Break instruction exception - code 80000003 (first chance)
A fatal system error has occurred.
Debugger entered on first try; Bugcheck callbacks have not been invoked.
A fatal system error has occurred.
nt!DbgBreakPointWithStatus:
fffff804`19410c50 cc int 3
kd> kp
# Child-SP RetAddr Call Site
00 fffff90e`a867e368 fffff804`19525382 nt!DbgBreakPointWithStatus
01 fffff90e`a867e370 fffff804`19524966 nt!KiBugCheckDebugBreak+0x12
02 fffff90e`a867e3d0 fffff804`19408eb7 nt!KeBugCheck2+0x946
03 fffff90e`a867eae0 fffff804`1941ad69 nt!KeBugCheckEx+0x107
04 fffff90e`a867eb20 fffff804`1941b190 nt!KiBugCheckDispatch+0x69
05 fffff90e`a867ec60 fffff804`19419523 nt!KiFastFailDispatch+0xd0
06 fffff90e`a867ee40 fffff804`1db3f677 nt!KiRaiseSecurityCheckFailure+0x323
07 fffff90e`a867efd0 fffff804`1daf6c05 HTTP!UlFreeUnknownCodingList+0x63
08 fffff90e`a867f000 fffff804`1dacd201 HTTP!UlpParseAcceptEncoding+0x299c5
09 fffff90e`a867f0f0 fffff804`1daa93d8 HTTP!UlAcceptEncodingHeaderHandler+0x51
0a fffff90e`a867f140 fffff804`1daa8ab7 HTTP!UlParseHeader+0x218
0b fffff90e`a867f240 fffff804`1da04c5f HTTP!UlParseHttp+0xac7
0c fffff90e`a867f3a0 fffff804`1da0490a HTTP!UlpParseNextRequest+0x1ff
0d fffff90e`a867f4a0 fffff804`1daa48c2 HTTP!UlpHandleRequest+0x1aa
0e fffff90e`a867f540 fffff804`1932ae85 HTTP!UlpThreadPoolWorker+0x112
0f fffff90e`a867f5d0 fffff804`19410408 nt!PspSystemThreadStartup+0x55
10 fffff90e`a867f620 00000000`00000000 nt!KiStartSystemThread+0x28
kd> !analyze -v
[...]
*************************************************************** ****************
* *
* Bugcheck Analysis *
* *
*******************************************************************************
KERNEL_SECURITY_CHECK_FAILURE (139)
A kernel component has corrupted a critical data structure. The corruption
could potentially allow a malicious user to gain control of this machine.
Arguments:
Arg1: 0000000000000003, A LIST_ENTRY has been corrupted (i.e. double remove).
Arg2: fffff90ea867ee40, Address of the trap frame for the exception that caused the BugCheck
Arg3: fffff90ea867ed98, Address of the exception record for the exception that caused the BugCheck
Arg4: 0000000000000000, Reserved