CVE-2026-62735

Information

• This vulnerability was originally discovered by Siyeon Wi. I reproduced the vulnerability independently for educational and case-study purposes.
• The vulnerability was also demonstrated at Pwn2Own Berlin 2026. References:
  • TrendAI Zero Day Initiative status
  • TrendAI Zero Day Initiative blog
• Microsoft update detail: CVE-2026-62735
• PoC has demonstrate crash by Integer Overflow vulnerability. With this vulnerability, we have primitive Heap Overflow -> SYSTEM shell.

Summary

• Vulnerability: Integer Overflow
• Component: http.sys
• Trigger function: UlpCreateInternalResponseOld
• Windows version: Windows 11 25H2 26200.8875

Detail

• The integer-overflow vulnerability occurs when calculating the total number of header bytes. As a result, http.sys allocates memory based on TotalHeaderBytes, even though the headers require a much larger buffer. This provides the basis for overflowing the nonpaged-pool allocation in UlGenerateMultipleKnownHeadersOld:

__int64 __fastcall UlpCreateInternalResponseOld(
    sv_UL_REQUEST *Request,
    unsigned __int16 EntityChunkCount,
    unsigned int FixedHeaderCount,
    unsigned int FixedHeaderBytes,
    unsigned int MultipleHeaderCount,
    unsigned int MultipleHeaderBytes,
    unsigned __int16 KnownHeaderCount,
    unsigned int TrailerCount,
    unsigned int TrailerBytes,
    char FastForwardRequested,
    char CacheEligible,
    char ResponseInfoPresent,
    char AutomaticChunkingRequired,
    char AdditionalHeaderRequired,
    sv_UL_INTERNAL_RESPONSE **InternalResponseOut)
{
    int VariableHeaderBytes; // r9d
    int H3ExtraHeaderBytes; // r10d
    unsigned int MultipleHeaderBytesLocal; // ecx
    unsigned int TotalHeaderBytes; // [rsp+E8h] [rbp+60h]
    ...
    // 0xffffff32 + 0x2e + 0 + 0xa0 = 0x4e
    TotalHeaderBytes = MultipleHeaderBytesLocal + FixedHeaderBytes + H3ExtraHeaderBytes + VariableHeaderBytes;
    ...
}

Crash log

• Bugcheck:

*** Fatal System Error: 0x00000050
                       (0xFFFFCD86AE712000,0x0000000000000002,0xFFFFF807489C4362,0x0000000000000002)

Driver at fault: 
***      HTTP.sys - Address FFFFF807489C4362 base at FFFFF80748860000, DateStamp 2bfcaa4c
.
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.

For analysis of this file, run !analyze -v
nt!DbgBreakPointWithStatus:
fffff807`b26fa0d0 cc              int     3

• Stack trace:

0: kd> k
 # Child-SP          RetAddr               Call Site
00 ffffe205`092ddf78 fffff807`b27afcf2     nt!DbgBreakPointWithStatus
01 ffffe205`092ddf80 fffff807`b27af21e     nt!KiBugCheckDebugBreak+0x12
02 ffffe205`092ddfe0 fffff807`b26f9357     nt!KeBugCheck2+0xb2e
03 ffffe205`092de770 fffff807`b24fd030     nt!KeBugCheckEx+0x107
04 ffffe205`092de7b0 fffff807`b2443c56     nt!MiSystemFault+0x850
05 ffffe205`092de8a0 fffff807`b28badcb     nt!MmAccessFault+0x646
06 ffffe205`092dea10 fffff807`489c4362     nt!KiPageFault+0x38b
07 ffffe205`092deba8 fffff807`489a6611     HTTP!memcpy+0x122
08 ffffe205`092debb0 fffff807`4897c165     HTTP!UlGenerateMultipleKnownHeadersOld+0xbdd
09 ffffe205`092ded90 fffff807`48976db0     HTTP!UlpPrepareHttpResponseOld+0x2c9
0a ffffe205`092dee70 fffff807`489361a4     HTTP!UlCaptureHttpResponseOld+0x92c
0b ffffe205`092defc0 fffff807`488f7c92     HTTP!UlSendHttpResponseIoctlOld+0x1160
0c ffffe205`092df600 fffff807`488c4db5     HTTP!UlSendHttpResponseIoctl+0x12
0d ffffe205`092df630 fffff807`b245cabb     HTTP!UxDeviceControl+0xb5
0e ffffe205`092df670 fffff807`b245ca33     nt!IopfCallDriver+0x5b
0f ffffe205`092df6b0 fffff807`b2ac0e75     nt!IofCallDriver+0x13
10 ffffe205`092df6e0 fffff807`b2abfcbc     nt!IopSynchronousServiceTail+0x1c5
11 ffffe205`092df790 fffff807`b2abf30e     nt!IopXxxControlFile+0x99c
12 ffffe205`092dfa00 fffff807`b28bf255     nt!NtDeviceIoControlFile+0x5e
13 ffffe205`092dfa70 00007ffa`d37c0144     nt!KiSystemServiceCopyEnd+0x25
14 00000014`0d9af2d8 00007ffa`d08a3953     ntdll!NtDeviceIoControlFile+0x14
15 00000014`0d9af2e0 00007ffa`d1f93335     KERNELBASE!DeviceIoControl+0x73
16 00000014`0d9af350 00007ff7`00cb1cb4     KERNEL32!DeviceIoControlImplementation+0x75
17 00000014`0d9af3a0 00000000`00001f7f     poc!main+0x924
18 00000014`0d9af3a8 00000000`00000007     0x1f7f
19 00000014`0d9af3b0 00000014`0d9af4a0     0x7
1a 00000014`0d9af3b8 00000000`00000000     0x00000014`0d9af4a0