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AUSCERT External Security Bulletin Redistribution
MFSA 2021-10 Security Vulnerabilities fixed in Firefox 87
24 March 2021
AusCERT Security Bulletin Summary
Operating System: UNIX variants (UNIX, Linux, OSX)
Impact/Access: Execute Arbitrary Code/Commands -- 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
Reduced Security -- Remote with User Interaction
CVE Names: CVE-2021-23988 CVE-2021-23987 CVE-2021-23986
CVE-2021-23985 CVE-2021-23984 CVE-2021-23983
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Mozilla Foundation Security Advisory 2021-10
Security Vulnerabilities fixed in Firefox 87
Announced: March 23, 2021
Fixed in: Firefox 87
# CVE-2021-23981: Texture upload into an unbound backing buffer resulted in an
A texture upload of a Pixel Buffer Object could have confused the WebGL code to
skip binding the buffer used to unpack it, resulting in memory corruption and a
potentially exploitable information leak or crash.
o Bug 1692832
# CVE-2021-23982: Internal network hosts could have been probed by a malicious
Reporter: Samy Kamkar, Ben Seri, and Gregory Vishnepolsky
Using techniques that built on the slipstream research, a malicious webpage
could have scanned both an internal network's hosts as well as services running
on the user's local machine utilizing WebRTC connections.
o Bug 1677046
# CVE-2021-23983: Transitions for invalid ::marker properties resulted in memory
Reporter: Irvan Kurniawan
By causing a transition on a parent node by removing a CSS rule, an invalid
property for a marker could have been applied, resulting in memory corruption
and a potentially exploitable crash.
o Bug 1692684
# CVE-2021-23984: Malicious extensions could have spoofed popup information
Reporter: Rob Wu
A malicious extension could have opened a popup window lacking an address bar.
The title of the popup lacking an address bar should not be fully controllable,
but in this situation was. This could have been used to spoof a website and
attempt to trick the user into providing credentials.
o Bug 1693664
# CVE-2021-23985: Devtools remote debugging feature could have been enabled
without indication to the user
Reporter: Anonymous working with Trend Micro's Zero Day Initiative
If an attacker is able to alter specific about:config values (for example
malware running on the user's computer), the Devtools remote debugging feature
could have been enabled in a way that was unnoticable to the user. This would
have allowed a remote attacker (able to make a direct network connection to the
victim) to monitor the user's browsing activity and (plaintext) network
traffic. This was addressed by providing a visual cue when Devtools has an open
o Bug 1659129
# CVE-2021-23986: A malicious extension could have performed credential-less
same origin policy violations
Reporter: Armin Razmjou
A malicious extension with the 'search' permission could have installed a new
search engine whose favicon referenced a cross-origin URL. The response to this
cross-origin request could have been read by the extension, allowing a
same-origin policy bypass by the extension, which should not have cross-origin
permissions. This cross-origin request was made without cookies, so the
sensitive information disclosed by the violation was limited to local-network
resources or resources that perform IP-based authentication.
o Bug 1692623
# CVE-2021-23987: Memory safety bugs fixed in Firefox 87 and Firefox ESR 78.9
Reporter: Mozilla developers and community
Mozilla developers and community members Matthew Gregan, Tyson Smith, Julien
Wajsberg, and Alexis Beingessner reported memory safety bugs present in Firefox
86 and Firefox ESR 78.8. 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 Firefox 87 and Firefox ESR 78.9
# CVE-2021-23988: Memory safety bugs fixed in Firefox 87
Reporter: Mozilla developers and community
Mozilla developers Tyson Smith and Christian Holler reported memory safety bugs
present in Firefox 86. 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 Firefox 87
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