Skip to content
Fencer Vulns
critical 9.8

CVE-2017-7821 json

A vulnerability where WebExtensions can download and attempt to open a file of some non-executable file types.

published 2018-06-11 8 y ago modified 2026-06-17 4 mo ago also EUVD-2017-16796

cvss
9.8
version 3.0, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.9%
EPSS 1.9% chance of exploitation in 30 days, percentile 79%
public exploits
0
none known

Summary

A vulnerability where WebExtensions can download and attempt to open a file of some non-executable file types. This can be triggered without specific user interaction for the file download and open actions. This could be used to trigger known vulnerabilities in the programs that handle those document types. This vulnerability affects Firefox < 56.

Patch / fix

  • Mozilla Firefox 56
  • firefox Ubuntu 14.04 LTS 56.0+build6-0ubuntu0.14.04.1
  • firefox Ubuntu 16.04 LTS 56.0+build6-0ubuntu0.16.04.1
  • firefox Ubuntu 18.04 LTS 56.0+build6-0ubuntu1

ubuntu advisories UBUNTU-CVE-2017-7821

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • firefox-esr openSUSE Tumbleweed 128.5.1-1.1
  • MozillaFirefox openSUSE Tumbleweed 92.0-1.2

opensuse advisories openSUSE-SU-2024:14572-1openSUSE-SU-2024:10600-1

Exploit prediction

1.91% chance of exploitation in the next 30 days, higher than 79% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • bugzilla.mozilla.org https://bugzilla.mozilla.org/show_bug.cgi?id=1346515 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.0 9.8 CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 7.5 AV:N/AC:L/Au:N/C:P/I:P/A:P

Affected products

  • Mozilla Firefox

Classification

Weakness
  • CWE-732 Incorrect Permission Assignment for Critical Resource

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.