Listen to this Post
How CVE-2026-55054 Works
CVE-2026-55054 is an out-of-bounds read vulnerability affecting Microsoft Office Excel, classified under CWE-125 (Out-of-bounds Read). The flaw resides in how Excel parses and processes specially crafted workbook files, specifically during the handling of certain data structures within the application’s memory management routines.
When Excel opens a maliciously crafted .xlsx or .xls file, the application attempts to read data from a memory buffer without properly validating the bounds of that buffer. Under normal operation, Excel’s parsing engine allocates fixed-size buffers to store cell data, formatting information, and other workbook elements. However, due to insufficient bounds checking in the vulnerable code path, the application may read past the end (or before the beginning) of the intended buffer.
The root cause is believed to involve an unknown function within Microsoft Office’s core processing logic that fails to validate input parameters before performing memory read operations. When an attacker crafts a workbook with specifically malformed records or structures, they can trigger this out-of-bounds read condition. The read operation may then expose adjacent memory contents—potentially including sensitive data such as heap metadata, portions of other documents recently processed by the application, or even memory addresses that could aid in further exploitation.
The attack vector is network-based (AV:N), requires no privileges (PR:N), but does demand user interaction (UI:R)—meaning a victim must open the malicious file, typically delivered via email attachment, malicious website download, or shared network drive. The vulnerability impacts confidentiality (C:H) as the primary security property, with no impact on integrity or availability.
Microsoft assigned a CVSS 3.1 base score of 6.5 (MEDIUM) to this vulnerability. The attack is considered easy to execute remotely, and no authentication is required for exploitation. As of the current disclosure, no technical details or public exploit code have been released, though the exploit market price is estimated between USD $5,000 and $25,000. The vulnerability affects a wide range of Microsoft Office products including Microsoft 365 Apps for Enterprise, Excel 2016, Office 2019, Office LTSC 2021/2024, and various Mac editions.
DailyCVE Form:
Platform: ……. Microsoft Office
Version: …….. 16.0–current
Vulnerability :…… Out-of-bounds Read
Severity: ……. MEDIUM (6.5)
date: ………. 2026-07-14
Prediction: …… 2026-08-15
What Undercode Say:
Analytics:
EPSS Score: 0.03% (low probability) SSVC Exploitation: none SSVC Automatable: no SSVC Technical Impact: partial Exploit Price Estimate: $5k-$25k CTI Interest Score: 0.69 Attack Vector: Network (AV:N) Attack Complexity: Low (AC:L) Privileges Required: None (PR:N) User Interaction: Required (UI:R) Confidentiality Impact: High (C:H)
Affected Products (from CPE enumeration):
cpe:2.3:a:microsoft:365_apps:-::::enterprise::x64: cpe:2.3:a:microsoft:365_apps:-::::enterprise::x86: cpe:2.3:a:microsoft:excel:2016::::::x64: cpe:2.3:a:microsoft:excel:2016::::::x86:
Exploit:
As of the current disclosure (July 2026), no public exploit code exists for CVE-2026-55054. Microsoft has not released technical details regarding the specific vulnerable code path. However, a theoretical exploit would involve the following approach:
1. Crafting a malicious Excel workbook containing malformed records designed to trigger the out-of-bounds read condition.
2. Delivering the file to the victim via phishing email, malicious website, or shared network drive.
3. Awaiting user interaction — the victim must open the file using a vulnerable version of Microsoft Office Excel.
4. Leaking memory contents — upon successful trigger, the out-of-bounds read would expose adjacent memory contents, potentially including sensitive data from other application contexts.
Hypothetical proof-of-concept structure (illustrative only): 1. Identify vulnerable parsing routine in Excel (unknown function) 2. Craft malformed BIFF/OOXML record with oversized length field 3. Trigger memmove/memcpy with invalid size parameter 4. Read out-of-bounds memory via the exposed data
Note: No working exploit is currently available, and the vulnerability is not considered automatable for large-scale attacks.
Protection:
- Apply Microsoft security updates as soon as they become available via the Microsoft Update Guide (https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55054).
- Enable Protected View in Microsoft Office — files from untrusted sources open in a restricted, read-only mode that limits exploitation surface.
- Disable automatic opening of macros and ActiveX controls in Excel.
- Implement email filtering to block suspicious .xlsx/.xls attachments from untrusted senders.
- Use Application Guard for Office (if available) to isolate untrusted documents in a containerized environment.
- Monitor for suspicious Excel processes reading abnormal memory regions using endpoint detection and response (EDR) tools.
Impact:
Successful exploitation of CVE-2026-55054 allows an unauthorized attacker to disclose sensitive information from the victim’s memory over a network. The confidentiality impact is rated HIGH, meaning that an attacker could potentially read:
– Heap metadata that could aid in further memory corruption exploits.
– Contents of other documents recently opened or processed by the same Excel instance.
– Sensitive user data such as passwords, cryptographic keys, or personally identifiable information (PII) that may reside in adjacent memory regions.
– Memory addresses that could be used to bypass Address Space Layout Randomization (ASLR) in subsequent attack stages.
The vulnerability does not affect integrity or availability, meaning it cannot be used to modify data or crash the application directly. However, as an information disclosure flaw, it serves as a critical stepping stone for more severe attacks—attackers can combine this read primitive with other vulnerabilities to achieve remote code execution or privilege escalation. The wide range of affected products (Microsoft 365 Apps, Excel 2016, Office 2019/2021/2024, and Mac editions) makes this vulnerability broadly impactful across enterprise and consumer environments.
🎯Let’s Practice Exploiting & Learn Patching For Free:
🎓 Live Courses & Certifications:
Join Undercode Academy for Verified Certifications
🚀 Request a Custom Project:
Secure, high-velocity infrastructure and disruptive technological engineering. Contact our engineering team for high-tier development and proprietary systems:
[email protected]
💎 Smart Architecture | 🛡️ Secure by Design | ⭐ Trusted by Thousands
Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
Undercode
