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CVE Record

CVE-2026-4720: Memory safety bugs fixed in Firefox ESR 140.9, Thunderbird ESR 140.9, Firefox 149 and Thunderbird 149

Memory safety bugs present in Firefox ESR 140.8, Thunderbird ESR 140.8, Firefox 148 and Thunderbird 148. 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. This vulnerability was fixed in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.

CriticalCVSS 9.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

Mozilla fixed critical memory safety defects in Firefox and Thunderbird. Mozilla says some bugs showed memory corruption and could potentially allow arbitrary code execution with enough effort. Organizations should treat outdated browser and mail-client installations as high-priority because compromise could affect user workstations and data.

Executive priority

Treat this as urgent patching for browsers and mail clients. There is no cited active exploitation, but the impact is potentially full code execution and the affected software is widely exposed to web and email content.

Technical view

CVE-2026-4720 covers memory safety bugs in Firefox 148, Firefox ESR 140.8, Thunderbird 148, and Thunderbird ESR 140.8. It is listed as CWE-120 with CVSS 9.8. Fixed versions are Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird ESR 140.9.

Likely exposure

Exposure is likely where managed or unmanaged endpoints run affected Mozilla Firefox or Thunderbird versions, including downstream Red Hat packaged builds covered by related errata or VEX records.

Exploitation context

The source bundle does not show KEV listing or active exploitation. Mozilla reports memory corruption evidence and states some bugs could be exploited to run arbitrary code with enough effort.

Researcher notes

Public details are grouped as memory safety bugs, with linked Mozilla Bugzilla IDs but no exploit mechanics in the source bundle. Avoid assuming exploitability beyond Mozilla's statement. Validate exact downstream package impact through Red Hat advisories and CSAF VEX.

Mitigation direction

  • Upgrade Firefox to 149 or Firefox ESR to 140.9 or later.
  • Upgrade Thunderbird to 149 or Thunderbird ESR to 140.9 or later.
  • Apply applicable Red Hat errata for downstream Mozilla packages.
  • Check Mozilla and Red Hat guidance for any product-specific exceptions.
  • Prioritize endpoints handling email, web browsing, or privileged administration.

Validation and detection

  • Inventory Firefox and Thunderbird versions across managed endpoints.
  • Confirm ESR channels are at 140.9 or later.
  • Confirm rapid-release channels are at 149 or later.
  • Review Red Hat errata and VEX status for Linux fleets.
  • Verify software management reports show successful update deployment.
Prepared
Confidence
high
Sources
12

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-120: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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description · low confidence lookup

Execution behavior lookup

The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.

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cve · low confidence lookup

CVE-2026-4720 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
Critical
CVSS
9.8 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
5Timeline events
2ADP providers
34Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: total

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
9.8CVSS 3.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H3.95.9CISA-ADP
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H1.65.9redhat-SADP

Vulnerability scoring details

Base CVSS 3.1 score

9.8Critical
CVSS 3.1 vector shape for CVE-2026-4720Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
cvssV3_1other:ssvc
redhat-SADPfirefox: thunderbird: Memory safety bugs fixed in Firefox ESR 140.9, Thunderbird ESR 140.9, Firefox 149 and Thunderbird 149
other:Red Hat severity ratingcvssV3_1
  • 2026-03-24T13:03:30.400Z: Reported to Red Hat.
  • 2026-03-24T12:30:43.271Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
MozillaFirefox140.9, 149Listed
MozillaThunderbird140.9, 149Listed
Weakness

CWE details

CWE-120

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-120 · source CWE mapping

Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')

Buffer Copy without Checking Size of Input ('Classic Buffer Overflow') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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