Threats / Microsoft / CVE-2021-42292

CVE-2021-42292 · EUVD no mirror located · GCVE no mirror located Verified 2026-09-19

Microsoft Office vulnerability

A security feature bypass in Microsoft Excel allows local users to execute arbitrary code, exploiting insufficient input validation in the application's security mechanisms.

Verdict

Today item — known-exploited.

This vulnerability enables privilege escalation and code execution on affected systems. The bypass of Excel's security features permits malicious actors to circumvent protections designed to prevent unauthorized script execution, leading to potential system compromise.

CISA KEV Yes · 2021-11-17⁵EPSS 0.43005 (verify live)⁶CVSS 7.8³CISA SSVC Exploitation: active · Automatable: no · Impact: total⁴

Is it exploitable?

— the evidence, ranked above the score

Reported exploitation

3 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.

docs.google.com ↗api.msrc.microsoft.com ↗cisa.gov ↗Confirmed

Exploited in the wild

Listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-17).

CISA KEV ↗Confirmed

Probability (EPSS)

EPSS 0.43005 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.

FIRST EPSS ↗High

Severity / affected

CVSS 7.8 (CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:P/RL:O/RC:C) · Affected: Microsoft, Office. Confirm exact fixed builds in the vendor advisory.CVSS — CNA-assigned (CVE.org), version 3.1, set at disclosure.

CVE.org ↗Reported

Weakness (CWE)

Mapped to CWE-357 CWE-357.CWE assignment from the public NVD record (may be stale); the weakness class drives how the flaw is exploited.

NVD ↗Reported

CISA SSVC (triage disposition)

Exploitation: active · Automatable: no · Technical Impact: totalCISA's own stakeholder-specific triage inputs, published in the CVE record (CISA Coordinator role). NOTE: this is CISA's three decision points; the final Act/Attend/Track decision also requires a Mission & Well-being input not published here, so no overall decision is asserted.

CISA-ADP ↗Reported

Currency of the record

CISA added this to its KEV catalog 7 days after the CVE record was published.KEV lag = CISA-KEV dateAdded − CVE.org datePublished; a floor on how long the known-exploited flaw sat in the public record before the federal catalog listed it. Severity/weakness here is CNA- or CISA-assigned (current at disclosure), independent of NVD's analysis backlog.

CISA KEV ↗CVE.org ↗Reported

WeaknessCWE-357 · CWE-357

Who’s exploiting it?

— attribution turns risk into urgency

Attribution not established

No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.

Why it matters

— the attack path, told twice: adversary, then board

Front door — unauthenticated access narrative 1

Attacker

I craft a malicious Excel document that bypasses the application's security feature restrictions.

Business

Users unknowingly open weaponized spreadsheets, exposing the organization to arbitrary code execution on employee workstations.

Keys to the kingdom — privilege/identity takeover narrative 2

Attacker

I deliver the document via email or file sharing, targeting users with local system access.

Business

The attack establishes a foothold within the corporate network, potentially enabling lateral movement and data exfiltration.

Lateral reach — past segmentation narrative 3

Attacker

I execute arbitrary code with the privileges of the user running Excel.

Business

Attackers gain access to sensitive files, credentials, and systems accessible to compromised user accounts.

What to do

— defensible action

Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.¹

Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.

Coverage & confidence

— what we know, and what we don’t

Established (cited)

KEV listing (CISA)

EPSS probability (FIRST)

3 reported-exploitation source(s)

CVSS 7.8 — CNA-assigned (CVE.org)

CISA SSVC triage disposition (CVE.org ADP)

CWE weakness mapping (NVD feed — CNA left none)

Catalogued by microsoft (CNA)

Named finder/reporter credit (CVE.org)

Coverage gaps — stated, not hidden

No EUVD / GCVE mirror in feed — single-authority dependency for the identifier.

EPSS & exposure are time-varying; verify live at the source.

Threat-actor attribution not established from feed data — absence of a name is not absence of compromise.

Disclosure & credit²

Catalogued by microsoftCNA

Credited with finding itMSTICfinder

Found an error? Propose a correction.

A correction is a cited counter-claim — it must cite a source, gets reviewed by a second human, and is never auto-applied. See the correction convention and our identity npub1j7gt9ky7sfcrjn8jjee6693dkzvk4rahs0fk2suu7968dfns62zs3mqm3y.

With JavaScript off: publish a signed kind 1111 Nostr event tagging ["r", "https://basicsecurity.net/threat/cve-2021-42292.html"], ["v", "sha256:34b30784797244f0a2dc6225545416fcb7f8b5d9c379b4d21f435a33ca4165e8"] (the record version), plus ["src", "<your source URL>"] and ["t", "correction"], per the correction convention. Our identity: npub1j7gt9ky7sfcrjn8jjee6693dkzvk4rahs0fk2suu7968dfns62zs3mqm3y. Cite-or-die: an event with no src is a coverage finding, not a proposal.