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AUSCERT External Security Bulletin Redistribution
MFSA 2020-52 Security Vulnerabilities fixed in Thunderbird 78.5
18 November 2020
AusCERT Security Bulletin Summary
Operating System: Windows
UNIX variants (UNIX, Linux, OSX)
Impact/Access: Execute Arbitrary Code/Commands -- Remote with User Interaction
Cross-site Scripting -- Remote with User Interaction
Denial of Service -- Remote with User Interaction
Provide Misleading Information -- Remote with User Interaction
Access Confidential Data -- Remote with User Interaction
CVE Names: CVE-2020-26968 CVE-2020-26966 CVE-2020-26965
CVE-2020-26961 CVE-2020-26960 CVE-2020-26959
CVE-2020-26958 CVE-2020-26956 CVE-2020-26953
CVE-2020-26951 CVE-2020-16012 CVE-2020-15999
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Mozilla Foundation Security Advisory 2020-52
Security Vulnerabilities fixed in Thunderbird 78.5
November 17, 2020
In general, these flaws cannot be exploited through email in the Thunderbird
product because scripting is disabled when reading mail, but are potentially
risks in browser or browser-like contexts.
# CVE-2020-26951: Parsing mismatches could confuse and bypass security
sanitizer for chrome privileged code
Irvan Kurniawan (@sourc7)
A parsing and event loading mismatch in Thunderbird's SVG code could have
allowed load events to fire, even after sanitization. An attacker already
capable of exploiting an XSS vulnerability in privileged internal pages could
have used this attack to bypass our built-in sanitizer.
o Bug 1667113
# CVE-2020-16012: Variable time processing of cross-origin images during
When drawing a transparent image on top of an unknown cross-origin image, the
Skia library drawImage function took a variable amount of time depending on the
content of the underlying image. This resulted in potential cross-origin
information exposure of image content through timing side-channel attacks.
o Bug 1642028
# CVE-2020-26953: Fullscreen could be enabled without displaying the security
Abdulrahman Alqabandi of Microsoft Browser Vulnerability Research
It was possible to cause the browser to enter fullscreen mode without
displaying the security UI; thus making it possible to attempt a phishing
attack or otherwise confuse the user.
o Bug 1656741
# CVE-2020-26956: XSS through paste (manual and clipboard API)
Irvan Kurniawan (@sourc7)
In some cases, removing HTML elements during sanitization would keep existing
SVG event handlers and therefore lead to XSS.
o Bug 1666300
# CVE-2020-26958: Requests intercepted through ServiceWorkers lacked MIME type
Thunderbird did not block execution of scripts with incorrect MIME types when
the response was intercepted and cached through a ServiceWorker. This could
lead to a cross-site script inclusion vulnerability, or a Content Security
o Bug 1669355
# CVE-2020-26959: Use-after-free in WebRequestService
During browser shutdown, reference decrementing could have occured on a
previously freed object, resulting in a use-after-free, memory corruption, and
a potentially exploitable crash.
o Bug 1669466
# CVE-2020-26960: Potential use-after-free in uses of nsTArray
If the Compact() method was called on an nsTArray, the array could have been
reallocated without updating other pointers, leading to a potential
use-after-free and exploitable crash.
o Bug 1670358
# CVE-2020-15999: Heap buffer overflow in freetype
Sergei Glazunov of Google Project Zero
In Freetype, if PNG images were embedded into fonts, the Load_SBit_Png function
contained an integer overflow that led to a heap buffer overflow, memory
corruption, and an exploitable crash.
Note: While Project Zero did discover instances of this vulnerability being
exploited in the wild against Chrome, in Thunderbird this vulnerability is only
triggerable if a rarely-used, hidden preference is toggled, and only affected
Linux and Android operating systems. Other operating systems are unaffected;
and Linux and Android are unaffected in the default configuration.
o Bug 1672223
# CVE-2020-26961: DoH did not filter IPv4 mapped IP Addresses
When DNS over HTTPS is in use, it intentionally filters RFC1918 and related IP
ranges from the responses as these do not make sense coming from a DoH
resolver. However when an IPv4 address was mapped through IPv6, these addresses
were erroneously let through, leading to a potential DNS Rebinding attack.
o Bug 1672528
# CVE-2020-26965: Software keyboards may have remembered typed passwords
Some websites have a feature "Show Password" where clicking a button will
change a password field into a textbook field, revealing the typed password.
If, when using a software keyboard that remembers user input, a user typed
their password and used that feature, the type of the password field was
changed, resulting in a keyboard layout change and the possibility for the
software keyboard to remember the typed password.
o Bug 1661617
# CVE-2020-26966: Single-word search queries were also broadcast to local
Searching for a single word from the address bar caused an mDNS request to be
sent on the local network searching for a hostname consisting of that string;
resulting in an information leak.
Note: This issue only affected Windows operating systems. Other operating
systems are unaffected.
o Bug 1663571
# CVE-2020-26968: Memory safety bugs fixed in Thunderbird 78.5
Mozilla developers and community
Mozilla developers Steve Fink, Jason Kratzer, Randell Jesup, Christian Holler,
and Byron Campen reported memory safety bugs present in Thunderbird 78.4. Some
of these bugs showed evidence of memory corruption and we presume that with
enough effort some of these could have been exploited to run arbitrary code.
o Memory safety bugs fixed in Thunderbird 78.5
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