CVE-2020-26950

critical

Published 2020-11-12 · Modified 2020-11-18

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CVSS v3

—

CVSS v4 NEW

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not yet in upstream

VIR risk

10.0

Description

In certain circumstances, the MCallGetProperty opcode can be emitted with unmet assumptions resulting in an exploitable use-after-free condition. This vulnerability affects Firefox < 82.0.3, Firefox ESR < 78.4.1, and Thunderbird < 78.4.2.

Predictions

Exploit likelihood

55%

Patch ETA

—

Heuristic predictions, AS-IS, for prioritization only.

Mitigations

No mitigations published for this CVE yet.

The vendor-content worker queues fetches as references arrive (check back in a few minutes). Or — if you've already worked around this in production — publish your fix to the community-verified tier.

✚ Propose a mitigation on Community → Mitigations published via the community go through AI scoring + 2 human reviewers + 7-day silent objection window before landing here with source_tier=community-verified.

Exploits

Public proof-of-concept code below. AS-IS, for defenders and authorised testing only.

Metasploit modules

exploit_multi/browser/firefox_jit_use_after_free rank

Firefox MCallGetProperty Write Side Effects Use After Free Exploit

Source fetch failed: fetch_error — view the original via the link above.

OS impact

SUSE Affected 1 release

Version	Status	Fixed in
—	Affected	—

Arch Fixed 1 release

Version	Status	Fixed in
—	Fixed	`82.0.3-1`

Debian Fixed 5 releases

Version	Status	Fixed in
trixie	Fixed	`78.4.1esr-1`
sid	Fixed	`82.0.3-1`
forky	Fixed	`78.4.1esr-1`
bullseye	Fixed	`78.4.1esr-1`
bookworm	Fixed	`78.4.1esr-1`

Red Hat Fixed 1 release

Version	Status	Fixed in
8	Fixed	—

References

Community-verified mitigations for this CVE will appear above when contributors publish them.

Verify integrity in audit chain (admin only). AS-IS.