CVE-2026-55039: Integer underflow (wrap or wraparound) in Microsoft Office Excel allows an unauthorized attacker to execute code locally.

highCVSS 7.8CVE-2026-55039

Integer underflow (wrap or wraparound) in Microsoft Office Excel allows an unauthorized attacker to execute code locally.

Details

Source: NVD Recent CVEs (US · database · site)
Severity: high — CVSS 7.8
Published: 2026-07-14
Last updated: 2026-07-16
Exploitation: Not in CISA KEV at last sync

Original advisory: https://nvd.nist.gov/vuln/detail/CVE-2026-55039

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-550390.30% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 23% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-55039	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

critical[NEW] [critical] Microsoft Office products: Multiple vulnerabilitiescert-bund
unknownexploitedNCSC-2026-0237 [1.02] [H/H] Vulnerabilities Fixed in Microsoft Officencsc-nl
unknownexploitedNCSC-2026-0237 [1.01] [H/H] Vulnerabilities fixed in Microsoft Officencsc-nl
unknownMultiple vulnerabilities in Microsoft Office (July 15, 2026)cert-fr-avis
unknownexploitedNCSC-2026-0237 [1.00] [M/H] Vulnerabilities fixed in Microsoft Officencsc-nl
highCVE-2026-55039: Microsoft Excel Remote Code Execution Vulnerabilitymsrc

Recent advisories for Integer underflow

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

mediumCVE-2026-63362: An unsigned integer underflow in the PubSub signature verification path in open62541 may allow…nvd · 2026-07-30
highCVE-2026-13308: Autel MaxiCharger AC Elite Home WebSockets Integer Underflow Remote Code Execution Vulnerabili…nvd · 2026-07-29
highCVE-2026-66729: facil.io 0.6.0 through 0.7.6 contains an integer underflow vulnerability in the multipart MIME…nvd · 2026-07-27
unknownCVE-2026-54890: Integer Underflow (Wrap or Wraparound) vulnerability in erlang otp erlang/otp (erts modules), …nvd · 2026-07-27
mediumCVE-2026-66337: A flaw was found in libsoup. An unsigned integer underflow in the soup_filter_input_stream_rea…nvd · 2026-07-24
highCVE-2026-66033: libssh2 through 1.11.1, fixed in commit a2ed82d, contains a pre-authentication integer underfl…nvd · 2026-07-24