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CVE Record

CVE-2026-2775: Mitigation bypass in the DOM: HTML Parser component

Mitigation bypass in the DOM: HTML Parser component. This vulnerability was fixed in Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.

CriticalCVSS 9.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

This is a critical Mozilla browser/mail-client flaw in the DOM HTML Parser. The source bundle says Mozilla fixed it in Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8. Treat unmanaged browser and Thunderbird versions as urgent patch targets.

Executive priority

Prioritize remediation now for managed browsers and Thunderbird. The severity and low attack requirements justify urgent patching, even though the provided sources do not show active exploitation.

Technical view

CVE-2026-2775 is described as a mitigation bypass in Mozilla’s DOM HTML Parser component and mapped to CWE-288. The supplied CVSS 3.1 vector is 9.8, with network attackability, low complexity, no privileges, no user interaction, and high confidentiality, integrity, and availability impact.

Likely exposure

Organizations are likely exposed where Firefox or Thunderbird are installed and not updated to the fixed Mozilla releases. Red Hat advisories indicate downstream package relevance. The bundle does not provide exact vulnerable version ranges beyond the fixed-release statements.

Exploitation context

The bundle marks KEV as false and provides no cited evidence of active exploitation. Public details appear limited; the Mozilla Bugzilla entry may not expose full technical detail. Do not assume exploitation is occurring without new vendor or KEV evidence.

Researcher notes

Evidence supports a critical mitigation-bypass issue in DOM HTML parsing, but public technical detail is sparse. Avoid inferring exploit primitives or affected version ranges beyond Mozilla’s fixed-version statements and Red Hat downstream advisories.

Mitigation direction

  • Update Firefox to 148, ESR 115.33, or ESR 140.8 as applicable.
  • Update Thunderbird to 148 or 140.8 as applicable.
  • Apply relevant Red Hat security advisories for packaged Mozilla components.
  • Check Mozilla and OS vendor guidance for any additional mitigations.
  • Prioritize managed endpoint browser and mail-client patch compliance.

Validation and detection

  • Inventory installed Firefox and Thunderbird versions across endpoints and servers.
  • Confirm deployed versions match or exceed the fixed releases named by Mozilla.
  • Review Red Hat advisory applicability for affected Linux fleets.
  • Check vulnerability scanners for CVE-2026-2775 after patch deployment.
  • Monitor CISA KEV and Mozilla advisories for exploitation-status changes.
Prepared
Confidence
medium
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-288: 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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cve · low confidence lookup

CVE-2026-2775 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
35Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: yesTechnical 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-2026-2775Attack 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: Mitigation bypass in the DOM: HTML Parser component
other:Red Hat severity ratingcvssV3_1
  • 2026-02-24T14:03:55.469Z: Reported to Red Hat.
  • 2026-02-24T13:33:11.553Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
MozillaFirefox115.33, 140.8, 148Listed
MozillaThunderbird140.8, 148Listed
Weakness

CWE details

CWE-288

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

CWE-288 · source CWE mapping

Authentication Bypass Using an Alternate Path or Channel

Authentication Bypass Using an Alternate Path or Channel represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs