CVE-2025-1942

CRITICALPre-NVD 9.89.8—
EchelonGraph scoreMEDIUM confidence

This critical-severity CVE scores 9.8 under the CNA's CVSS (NVD's own analysis pending). EPSS exploit probability: 0.4%, top 64% of all CVEs by exploit prediction. GitHub Security Advisory enrichment pending alignment with NVD CVSS.

Triggered by: NVD CVSS baseline
Sources: cna:mozilla, epss, ghsa
9.8
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 0%CVSS: 9.8Exploit: NoneExposed: 0

A fix is available — apply it.

When String.toUpperCase() caused a string to get longer it was possible for uninitialized memory to be incorporated into the result string. This vulnerability was fixed in Firefox 136 and Thunderbird 136.

CVSS v3
9.8
EG Score
9.8(medium)
EG Risk
59(Track)
EG Risk 59/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity98% × 45%
Exploitation0% × 40%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS
36.4%
KEV
Not listed

Published

March 4, 2025

Last Modified

June 4, 2026

Advisory Details (3)

Auto-updated Jun 20, 2026
No patch confirmed yet.
generic

Security Vulnerabilities fixed in Thunderbird 136 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2025-17/
generic

Security Vulnerabilities fixed in Firefox 136 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2025-14/
generic

1947139 - (CVE-2025-1942) A bug in toUpperCase string chars reallocation

https://bugzilla.mozilla.org/show_bug.cgi?id=1947139

Patch Availability(2)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntufirefox-mozsymbols (136.0+build3-0ubuntu0.20.04.1) @ focal2026-05-21ubuntu
ubuntuxul-ext-lightning (1:140.7.1+build1-0ubuntu0.22.04.1) @ jammy2026-05-21ubuntu

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

All Vendor Advisories

(2)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 11× in last 7d / 42× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 119 total refreshes for this CVE.

  1. 2026-07-24 14:16 UTCEPSS rescore
  2. 2026-07-23 14:17 UTCEPSS rescore
  3. 2026-07-23 02:49 UTCEG score recompute▲ 3.30
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Frequently asked(5)

What is CVE-2025-1942?
CVE-2025-1942 is a critical vulnerability published on March 4, 2025. When String.toUpperCase() caused a string to get longer it was possible for uninitialized memory to be incorporated into the result string. This vulnerability was fixed in Firefox 136 and Thunderbird 136.
When was CVE-2025-1942 disclosed?
CVE-2025-1942 was first published in the National Vulnerability Database on March 4, 2025, with the most recent update on June 4, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2025-1942 actively exploited?
CVE-2025-1942 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 36.4% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2025-1942?
CVE-2025-1942 has a CVSS v4.0 base score of 9.8 (CNA self-assessment; NVD's own analysis pending).
How do I remediate CVE-2025-1942?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2025-1942, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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