Arbitrary JavaScript execution in internal pages via Reader View JSON-LD injection

published 2026-06-01 5 mo ago modified 2026-07-22 3 mo ago also EUVD-2026-33630

cvss: 5.4; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.2%; EPSS 0.2% chance of exploitation in 30 days, percentile 4%
public exploits: 0; none known

Firefox for iOS Reader View did not properly escape HTML tags in JSON-LD metadata. A malicious page could inject markup that changed Reader View behavior and leaked sensitive URL parameters. These parameters could then be used to access internal pages, potentially resulting in arbitrary JavaScript execution in an internal origin. This vulnerability was fixed in Firefox for iOS 151.2.

Patch / fix

fixed in 1

mozilla firefox 151.2

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 5 mo ago (2026-06-01)

Exploit prediction

0.16% chance of exploitation in the next 30 days, higher than 4% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CISA ADP	3.1	5.4	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
CNA	3.1	5.4	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N

Affected products

Mozilla Firefox for iOS

Classification

Weakness

CWE-79 Improper Neutralization of Input During Web Page Generation

References

mozilla.org /security/advisories/mfsa2026-53/
vendor-advisory
bugzilla.mozilla.org /show_bug.cgi?id=2036573
permissions-required

Sources

CVE List CVE-2026-9309
NVD CVE-2026-9309

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.

Summary