The "instanceof" operator can bypass the Xray wrapper mechanism. When called on web content from the browser itself or an extension the web content can provide its own result for that operator, possibly tricking the browser or extension into mishandling the element. This vulnerability affects Firefox < 56.

Versions of Mozilla Firefox earlier than 56 are unpatched for the following vulnerabilities :

 - An unspecified flaw exists that is triggered as certain input is not properly validated. This may allow a context-dependent attacker to corrupt memory and potentially execute arbitrary code. No further details have been provided by the vendor.
 - A flaw exists in the 'js::AddPropertyTypesAfterProtoChange()' function in 'js/src/vm/NativeObject.cpp' that is triggered when handling the 'unknown-properties' flag. This may allow a context-dependent attacker to corrupt memory and potentially execute arbitrary code.
 - A flaw exists in 'layout/style/nsCSSPseudoElements.cpp' that is triggered when handling pseudo-element atoms. This may allow a context-dependent attacker to corrupt memory and potentially execute arbitrary code.
 - An unspecified flaw exists that is triggered as certain input is not properly validated. This may allow a context-dependent attacker to corrupt memory and potentially execute arbitrary code. No further details have been provided by the vendor.
 - A flaw exists in 'dom/base/nsDocument.cpp' that is triggered when handling intersection observers. This may allow a context-dependent attacker to corrupt memory and potentially execute arbitrary code.
 - A flaw exists in the 'LayerTransactionParent::Destroy()' function in 'gfx/layers/ipc/LayerTransactionParent.cpp' that is triggered as certain input is not properly validated. This may allow a context-dependent attacker to corrupt memory and potentially execute arbitrary code.
 - An overflow condition exists in the 'FPSCounter::PrintHistogram()' function in 'gfx/layers/composite/FPSCounter.cpp' that is triggered as certain input is not properly validated. This may allow a context-dependent attacker to cause a buffer overflow and potentially execute arbitrary code.
 - A flaw exists in the 'FlagAllOperandsAsHavingRemovedUses()' function in 'js/src/jit/IonAnalysis.cpp' that is triggered as certain input is not properly validated. This may allow a context-dependent attacker to corrupt memory and potentially execute arbitrary code.
 - A flaw exists in 'memory/mozjemalloc/mozjemalloc.cpp' that is triggered as certain input is not properly validated. This may allow a context-dependent attacker to corrupt memory and potentially execute arbitrary code.
 - A flaw exists in the 'ReadCompressedIndexDataValuesFromBlob()' function in 'dom/indexedDB/ActorsParent.cpp' that is triggered as certain input is not properly validated. This may allow a context-dependent attacker to corrupt memory and potentially execute arbitrary code.
 - An unspecified flaw exists that is triggered as certain input is not properly validated. This may allow a context-dependent attacker to corrupt memory and potentially execute arbitrary code. No further details have been provided by the vendor.
 - An unspecified flaw exists that is triggered as certain input is not properly validated. This may allow a context-dependent attacker to corrupt memory and potentially execute arbitrary code. No further details have been provided by the vendor.
 - A flaw exists in 'js/src/vm/StructuredClone.cpp' that is triggered when handling structured clone reads. This may allow a context-dependent attacker to corrupt memory and potentially execute arbitrary code.
 - An unspecified flaw exists that is triggered as certain input is not properly validated. This may allow a context-dependent attacker to corrupt memory and potentially execute arbitrary code. No further details have been provided by the vendor.
 - A flaw exists in 'editor/libeditor/HTMLEditor.cpp' that is triggered when handling root elements in the editor. This may allow a context-dependent attacker to corrupt memory and potentially execute arbitrary code.
 - A flaw exists in 'dom/media/GraphDriver.cpp' that is triggered when handling errors. This may allow a context-dependent attacker to corrupt memory and potentially execute arbitrary code.
 - An overflow condition exists in the 'hnj_hyphen_hyphword()' function in 'hyphen.c' that is triggered as certain input is not properly validated. This may allow a context-dependent attacker to cause a buffer overflow and potentially execute arbitrary code within a process linked against the library.
 - A flaw exists in the 'EditorBase::FinalizeSelection()' function in 'editor/libeditor/EditorBase.cpp' that is triggered as certain input is not properly validated. This may allow a context-dependent attacker to corrupt memory and potentially execute arbitrary code.
 - A flaw exists in the 'DocAccessible::DoARIAOwnsRelocation()' function in 'accessible/generic/DocAccessible.cpp' that is triggered as certain input is not properly validated. This may allow a context-dependent attacker to corrupt memory and potentially execute arbitrary code.
 - An unspecified flaw exists that is triggered as certain input is not properly validated. This may allow a context-dependent attacker to corrupt memory and potentially execute arbitrary code. No further details have been provided by the vendor.
 - A use-after-free condition exists in the Fetch API related to missing thread safety. This may allow a context-dependent attacker to dereference already freed memory and potentially execute arbitrary code.
 - A flaw exists that is triggered when pages enter fullscreen mode without user notification. This allows a context-dependent attacker to spoof the address bar.
 - A use-after-free error exists in 'accessible/generic/DocAccessible.cpp' that is triggered when manipulating Accessible Rich Internet Applications (ARIA) elements. This may allow a context-dependent attacker to dereference already freed memory and potentially execute arbitrary code.
 - A use-after-free error exists in design mode that is triggered when objects are resized. This may allow a context-dependent attacker to dereference already freed memory and potentially execute arbitrary code.
 - A use-after-free error exists in the 'ssl3_HandleCertificateVerify()' function in 'lib/ssl/ssl3con.c' that is triggered when handling handshake hashes during TLS '1.2' exchanges. This may allow a context-dependent attacker to dereference already freed memory and potentially execute arbitrary code.
 - A flaw exists that is triggered as the content principal is not properly checked when handling drag and drop actions onto the browser UI. With specially crafted web content including file: URLs, a context-dependent attacker can open local files.
 - A flaw exists in the PendingLookup class in 'toolkit/components/downloads/ApplicationReputation.cpp' that is triggered when handling downloads encoded with data: and blob: URL elements. This may allow a context-dependent attacker to bypass the phishing and malware protection feature.
 - An integer truncation flaw exists in the JavaScript parser that may allow a context-dependent attacker to potentially disclose memory contents.
 - A flaw exists in the 'MacOSFontEntry::ReadCMAP()' function in 'gfx/thebes/gfxMacPlatformFontList.mm' that is triggered as certain tibetan and arabic unicode characters are displayed as whitespace in combination with macOS fonts. With a specially crafted IDN domain, a context-dependent attacker can spoof a valid URL and conduct phishing attacks.
 - A flaw exists that is triggered when creating a modal dialog using the data: protocol via JavaScript. With a specially crafted web page, a context-dependent attacker can spoof the origin of the modal dialog.
 - A flaw exists in the WebExtensions component that is triggered when handling popups and panels in the extension UI. This may allow a context-dependent attacker to load an 'about:' URL.
 - A flaw exists in the WebExtensions component that is triggered when handling file downloads. This may allow a context-dependent attacker to download and open files without user interaction.
 - A flaw exists in the 'nsDocument::InitCSP()' function in 'dom/base/nsDocument.cpp' that is triggered as the sandbox directive does not create unique origin. This may result in incorrect enforcement of the content security policy (CSP).
 - A flaw exists in the WebCrypto API that is triggered as the AES-GCM implementation allows a zero-length IV. This may allow a context-dependent attacker to determine the authentication key.
 - A flaw exists that is is triggered as results of the 'instanceof' operator can be manipulated. With specially crafted web content, a context-dependent attacker can bypass the Xray wrapper mechanism.
 - An unspecified flaw exists that is triggered when drawing and validating elements with the ANGLE graphics library. This may allow a context-dependent attacker to cause a buffer overflow, potentially allowing the execution of arbitrary code.
 - A flaw exists related to speculative execution, which is used as a performance feature to speed up operations. This optimization can result in memory being cached during indirect branch prediction. This may allow a local attacker to train the Branch Target Buffer (BTB) to trigger a false prediction to a specially crafted memory location, causing a speculative execution of a crafted gadget and the caching of arbitrary memory. Using a side-channel attack on the cache the attacker can disclose parts of the privileged kernel memory.

The version of Mozilla Firefox installed on the remote Windows host is prior to 56. It is, therefore, affected by multiple vulnerabilities, some of which allow code execution and potentially exploitable crashes.

The version of Mozilla Firefox installed on the remote macOS or Mac OS X host is prior to 56. It is, therefore, affected by multiple vulnerabilities, some of which allow code execution and potentially exploitable application crashes.

The remote Ubuntu 14.04 LTS / 16.04 LTS host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-3435-1 advisory.

    Multiple security issues were discovered in Firefox. If a user were tricked in to opening a specially     crafted website, an attacker could potentially exploit these to read uninitialized memory, obtain     sensitive information, bypass phishing and malware protection, spoof the origin in modal dialogs, conduct     cross-site scripting (XSS) attacks, cause a denial of service via application crash, or execute arbitrary     code. (CVE-2017-7793, CVE-2017-7810, CVE-2017-7811, CVE-2017-7812, CVE-2017-7813, CVE-2017-7814,     CVE-2017-7815, CVE-2017-7818, CVE-2017-7819, CVE-2017-7820, CVE-2017-7822, CVE-2017-7823, CVE-2017-7824)

    Martin Thomson discovered that NSS incorrectly generated handshake hashes. A remote attacker could     potentially exploit this to cause a denial of service via application crash, or execute arbitrary code.
    (CVE-2017-7805)

    Multiple security issues were discovered in WebExtensions. If a user were tricked in to installing a     specially crafted extension, an attacker could potentially exploit these to download and open non-     executable files without interaction, or obtain elevated privileges. (CVE-2017-7816, CVE-2017-7821)

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

Mozilla Foundation reports :

CVE-2017-7793: Use-after-free with Fetch API

CVE-2017-7817: Firefox for Android address bar spoofing through fullscreen mode

CVE-2017-7818: Use-after-free during ARIA array manipulation

CVE-2017-7819: Use-after-free while resizing images in design mode

CVE-2017-7824: Buffer overflow when drawing and validating elements with ANGLE

CVE-2017-7805: Use-after-free in TLS 1.2 generating handshake hashes

CVE-2017-7812: Drag and drop of malicious page content to the tab bar can open locally stored files

CVE-2017-7814: Blob and data URLs bypass phishing and malware protection warnings

CVE-2017-7813: Integer truncation in the JavaScript parser

CVE-2017-7825: OS X fonts render some Tibetan and Arabic unicode characters as spaces

CVE-2017-7815: Spoofing attack with modal dialogs on non-e10s installations

CVE-2017-7816: WebExtensions can load about: URLs in extension UI

CVE-2017-7821: WebExtensions can download and open non-executable files without user interaction

CVE-2017-7823: CSP sandbox directive did not create a unique origin

CVE-2017-7822: WebCrypto allows AES-GCM with 0-length IV

CVE-2017-7820: Xray wrapper bypass with new tab and web console

CVE-2017-7811: Memory safety bugs fixed in Firefox 56

CVE-2017-7810: Memory safety bugs fixed in Firefox 56 and Firefox ESR 52.4

ID	Name	Product	Family	Severity
700321	Mozilla Firefox < 56 Multiple Vulnerabilities	Nessus Network Monitor	Web Clients	high
103680	Mozilla Firefox < 56 Multiple Vulnerabilities	Nessus	Windows	critical
103678	Mozilla Firefox < 56 Multiple Vulnerabilities (macOS)	Nessus	MacOS X Local Security Checks	critical
103646	Ubuntu 14.04 LTS / 16.04 LTS : Firefox vulnerabilities (USN-3435-1)	Nessus	Ubuntu Local Security Checks	critical
103556	FreeBSD : mozilla -- multiple vulnerabilities (1098a15b-b0f6-42b7-b5c7-8a8646e8be07)	Nessus	FreeBSD Local Security Checks	critical

Detections

Analytics

CVE-2017-7820

medium

Tenable Plugins

high

critical

critical

critical

critical