OnlyPatch
Windows Cryptographic Services

CVE-2023-36906 — Windows Cryptographic Services Information Disclosure Vulnerability

Important CVSS 7.5 EPSS 0.01973 🔬 Patch diffed 2023-08 archive

Executive Summary

None

Overview

7.5
CVSS HIGH
Important
MS Severity
Not Exploited
MS Exploit Status
Less Likely
MS Exploit Likelihood
Category Information Disclosure
Weakness CWE-170: Improper Null Termination
Released Aug 8 2023
Last Updated Aug 8 2023
Publicly Disclosed No
CISA KEV Not Listed
Known Exploits None Known
EPSS Score 0.01973 — 0.78687 percentile
NVD CVSS 7.5 HIGH — differs from MSRC

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C
ATTACK VECTOR
Network
ATTACK COMPLEXITY
Low
PRIVILEGES REQUIRED
None
USER INTERACTION
None
SCOPE
Unchanged
CONFIDENTIALITY
High
INTEGRITY
None
AVAILABILITY
None
EXPLOIT CODE MATURITY
Unproven
REMEDIATION LEVEL
Official Fix
REPORT CONFIDENCE
Confirmed
Temporal Score: 4.8

EPSS Score

0.01973
probability of exploitation in the next 30 days
0.78687 percentile - updated 2026-08-14
View on FIRST.org

Affected Products

21 affected products
Product KB Article Severity Impact Restart Required
Windows 10 for 32-bit Systems 5029259 (Security Update) Important Information Disclosure Yes
Windows 10 for x64-based Systems 5029259 (Security Update) Important Information Disclosure Yes
Windows 10 Version 1607 for 32-bit Systems 5029242 (Security Update) Important Information Disclosure Yes
Windows 10 Version 1607 for x64-based Systems 5029242 (Security Update) Important Information Disclosure Yes
Windows 10 Version 1809 for 32-bit Systems 5029247 (Security Update) Important Information Disclosure Yes
Windows 10 Version 1809 for ARM64-based Systems 5029247 (Security Update) Important Information Disclosure Yes
Windows 10 Version 1809 for x64-based Systems 5029247 (Security Update) Important Information Disclosure Yes
Windows 10 Version 21H2 for 32-bit Systems 5029244 (Security Update) Important Information Disclosure Yes
Windows 10 Version 21H2 for ARM64-based Systems 5029244 (Security Update) Important Information Disclosure Yes
Windows 10 Version 21H2 for x64-based Systems 5029244 (Security Update) Important Information Disclosure Yes
Windows 10 Version 22H2 for 32-bit Systems 5029244 (Security Update) Important Information Disclosure Yes
Windows 10 Version 22H2 for ARM64-based Systems 5029244 (Security Update) Important Information Disclosure Yes
Windows 10 Version 22H2 for x64-based Systems 5029244 (Security Update) Important Information Disclosure Yes
Windows 11 version 21H2 for ARM64-based Systems 5029253 (Security Update) Important Information Disclosure Yes
Windows 11 version 21H2 for x64-based Systems 5029253 (Security Update) Important Information Disclosure Yes
Windows 11 Version 22H2 for ARM64-based Systems 5029263 (Security Update) Important Information Disclosure Yes
Windows 11 Version 22H2 for x64-based Systems 5029263 (Security Update) Important Information Disclosure Yes
Windows Server 2008 for 32-bit Systems Service Pack 2 5029318 (Monthly Rollup) 5029301 (Security Only) Important Information Disclosure 5028222 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.0.6003.22216 Yes 5029318 5029301 Windows Server 2008 for 32-bit Systems Service Pack 2 (Server Core installation) 5029318 (Monthly Rollup) 5029301 (Security Only) Important Information Disclosure 5028222 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.0.6003.22216 Yes 5029318 5029301 Windows Server 2008 for x64-based Systems Service Pack 2 5029318 (Monthly Rollup) 5029301 (Security Only) Important Information Disclosure 5028222 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.0.6003.22216 Yes 5029318 5029301 Windows Server 2008 for x64-based Systems Service Pack 2 (Server Core installation) 5029318 (Monthly Rollup) 5029301 (Security Only) Important Information Disclosure 5028222 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.0.6003.22216 Yes 5029318 5029301 Windows Server 2008 R2 for x64-based Systems Service Pack 1 5029296 (Monthly Rollup) 5029307 (Security Only) Important Information Disclosure 5028240 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.1.7601.26664 Yes 5029296 5029307 Windows Server 2008 R2 for x64-based Systems Service Pack 1 (Server Core installation) 5029296 (Monthly Rollup) 5029307 (Security Only) Important Information Disclosure 5028240 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.1.7601.26664 Yes 5029296 5029307 Windows Server 2012 5029295 (Monthly Rollup) 5029308 (Security Only) Important Information Disclosure 5028232 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.2.9200.24414 Yes None Windows Server 2012 (Server Core installation) 5029295 (Monthly Rollup) 5029308 (Security Only) Important Information Disclosure 5028232 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.2.9200.24414 Yes None Windows Server 2012 R2 5029312 (Monthly Rollup) 5029304 (Security Only) Important Information Disclosure 5028228 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.3.9600.21503 Yes None Windows Server 2012 R2 (Server Core installation) 5029312 (Monthly Rollup) 5029304 (Security Only) Important Information Disclosure 5028228 Base: 5.5 Temporal: 4.8 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C 6.3.9600.21503 Yes None Windows Server 2016 5029242 (Security Update) Important Information Disclosure Yes
Windows Server 2016 (Server Core installation) 5029242 (Security Update) Important Information Disclosure Yes
Windows Server 2019 5029247 (Security Update) Important Information Disclosure Yes
Windows Server 2019 (Server Core installation) 5029247 (Security Update) Important Information Disclosure Yes

Patches

6 patches
Article Type Restart
5029259 Security Update Yes
5029242 Security Update Yes
5029247 Security Update Yes
5029244 Security Update Yes
5029253 Security Update Yes
5029263 Security Update Yes

Patch Diff

ghidriff · ncryptprov.dll (KB5029263)

Out-of-bounds read / information disclosure (CWE-170 Improper Null Termination) in the Microsoft Software Key Storage Provider ncryptprov.dll, reachable from an AppContainer sandbox via the CNG Key Isolation RPC (keyiso.dll in lsass). The client-defined 'Use Context' provider property is stored by SPCryptSetProviderProperty at exactly the client-supplied length with NO null terminator, but read back by SPCryptGetProviderProperty as a wide string: `do { ++i; } while (*(WORD*)(buf + 2*i));` scans for a NUL with no bound, then memcpy returns 2*i+2 bytes. If the stored content has no embedded null, the scan runs past the allocation and returns adjacent lsass heap to the caller. k0shl used this to leak a provider-object pointer (defeating ASLR/CFG) to bootstrap the CVE-2023-28229 CNG UAF into lsass code execution / sandbox escape. IN-HOUSE ghidriff of ncryptprov.dll 10.0.22621.1928 -> .2134 (Aug 8 2023) confirms the fix: SPCryptSetProviderProperty now bounds-checks size (<= 0x7ffffffd), allocates _Size+2, and writes a 0x0000 WCHAR terminator at buf[_Size & ~1] before memcpy - so the stored property is always NUL-terminated and the read-side scan stays in bounds. SPCryptSetKeyProperty gets the same hardening (5% match). Unconditional fix (no feature flag). keyiso.dll was RULED OUT: SrvCryptGetProviderProperty is byte-identical across .819/.1555/.1992. Credit: k0shl of Kunlun Lab. Chains with CVE-2023-28229.

Pre-patch version 10.0.22621.1928 Download
Post-patch version 10.0.22621.2134 Download
Function Address Change Note
SPCryptSetProviderProperty 96% match code (null-termination + bound added, unconditional) Pre: RtlAllocateHeap(_, 0, _Size) stores the client 'Use Context' buffer with no terminator. Post: adds `if (param_3 == 0 || 0x7ffffffd < uVar3) goto error`, allocates `_Size + 2`, writes `*(WORD*)(buf + (param_4 & 0xfffffffe)) = 0` (NUL terminator), then memcpy(buf, param_3, _Size). Guarantees the stored property is NUL-terminated so the SPCryptGetProviderProperty read-back scan cannot over-read.
SPCryptSetKeyProperty 5% match (heavily rewritten) code (same null-termination hardening for key properties) Rewritten alongside the provider-property fix to apply the same terminate-on-store handling to the key-property path.
SPCryptGetProviderProperty unchanged (read/leak site) vulnerable sink (not modified) Reads the stored property as a wide string, scanning for a NUL with no bound (do{++i;}while(*(WORD*)(buf+2*i))) then memcpy 2*i+2 bytes. The fix is on the store side, so this read site is unchanged - which is why a read-side-only or keyiso-only search misses the fix.
View full diff report View RCA report

Attack Path

A 'Use Context' KSP property is stored without a null terminator, so reading it back as a string over-reads adjacent lsass heap

Attack path for CVE-2023-36906 A 'Use Context' KSP property is stored without a null terminator, so reading it back as a string over-reads adjacent lsass heap 01 — ENTRY Sandboxed (AppContainer) process reaches the CNG Key Isolation RPC in lsass keyiso.dll (CNG Key Isolation, in lsass) exposes provider-property RPCs reachable from AppContainer / restricted tokens (browser / Adobe Reader renderer). These wrap the Microsoft KSP ncryptprov.dll. 02 — CONTROLLED INPUT Stores a 'Use Context' provider property with client-controlled size and content SPCryptSetProviderProperty(provider, 'Use Context', buf[N]) allocates exactly N bytes and copies the client content - the caller controls both size and bytes, and can omit any embedded null. 03 — PATH Queries the property back; SPCryptGetProviderProperty reads it as a wide string The read computes length by scanning for a NUL: `do { ++i; } while (*(WORD*)(buf + 2*i));` then memcpy returns 2*i+2 bytes to the caller. 04 — MISSING CHECK The stored buffer has no null terminator, so the NUL-scan runs past its end Store length != read termination. With no embedded null, the scan walks off the allocation (CWE-170) and the copy length exceeds the buffer. 05 — PRIMITIVE Out-of-bounds read of adjacent lsass heap -> ASLR/CFG leak -> chains to EoP The over-read returns neighbouring heap to the sandboxed caller. Groomed next to a memory-buffer object it leaks a provider-object pointer, defeating lsass ASLR/CFG - the leak that makes CVE-2023-28229 (CNG UAF) exploitable into lsass code execution. The Aug 2023 fix null-terminates the stored property (allocate _Size+2, write L'\0'); unconditional, no feature flag.

Derived from the patch delta: the checks added by the vendor identify which fields crossed a trust boundary unvalidated. Reachability and privilege are taken from the call chain in the RCA report.

Known Exploits

Acknowledgments

k0shl

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