Loading vulnerability…
CVE-2026-20957 is a critical remote code execution vulnerability in Microsoft Excel caused by an integer underflow during processing of crafted spreadsheet content. Available reporting indicates the underflow can lead to a heap-based buffer overflow while Excel parses a specially crafted file. Successful exploitation results in code execution in the security context of the logged-on user.
Mallory correlates every CVE against your assets, your vendors, and active adversary campaigns. Know which vulnerabilities matter for you, not just which ones are loud.
What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
What an attacker gets, and what they’ve been doing with it.
If you can’t patch tonight, do this now.
Patch, then assume compromise.
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
13 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
Critical Microsoft Excel remote code execution via maliciously crafted Office files (memory-related) per the content.
A Microsoft Excel remote code execution vulnerability where an integer underflow can lead to a heap-based buffer overflow, enabling arbitrary code execution when a user opens a crafted spreadsheet.
A Microsoft Excel remote code execution vulnerability where an integer underflow can lead to a heap-based buffer overflow, enabling arbitrary code execution when a user opens a crafted spreadsheet.
A remote code execution vulnerability in Microsoft Excel, likely triggerable via specially crafted spreadsheets.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.