CVE-2026-26129 Vulnerability Analysis & Exploit Details

CVE-2026-26129
Vulnerability Scoring

7.5
/10
Very High Risk

Highly exploitable, CVE-2026-26129 poses a critical security risk that could lead to severe breaches.

Attack Complexity Details

  • Attack Complexity: Low
    Exploits can be performed without significant complexity or special conditions.
  • Attack Vector: Network
    Vulnerability is exploitable over a network without physical access.
  • Privileges Required: None
    No privileges are required for exploitation.
  • Scope: Unchanged
    Exploit remains within the originally vulnerable component.
  • User Interaction: None
    No user interaction is necessary for exploitation.

CVE-2026-26129 Details

Status: Analyzed

Last updated: 🕢 08 May 2026, 19:53 UTC
Originally published on: 🕙 07 May 2026, 22:16 UTC

CVSS Release: version 3

CVSS3 Source

secure@microsoft.com

CVSS3 Type

Primary

CVSS3 Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

CVE-2026-26129 Vulnerability Summary

CVE-2026-26129: Improper neutralization of special elements in M365 Copilot allows an unauthorized attacker to disclose information over a network.

Assessing the Risk of CVE-2026-26129

Access Complexity Graph

The exploitability of CVE-2026-26129 depends on two key factors: attack complexity (the level of effort required to execute an exploit) and privileges required (the access level an attacker needs).

Exploitability Analysis for CVE-2026-26129

With low attack complexity and no required privileges, CVE-2026-26129 is an easy target for cybercriminals. Organizations should prioritize immediate mitigation measures to prevent unauthorized access and data breaches.

Understanding AC and PR

A lower complexity and fewer privilege requirements make exploitation easier. Security teams should evaluate these aspects to determine the urgency of mitigation strategies, such as patch management and access control policies.

Attack Complexity (AC) measures the difficulty in executing an exploit. A high AC means that specific conditions must be met, making an attack more challenging, while a low AC means the vulnerability can be exploited with minimal effort.

Privileges Required (PR) determine the level of system access necessary for an attack. Vulnerabilities requiring no privileges are more accessible to attackers, whereas high privilege requirements limit exploitation to authorized users with elevated access.

CVSS Score Breakdown Chart

Above is the CVSS Sub-score Breakdown for CVE-2026-26129, illustrating how Base, Impact, and Exploitability factors combine to form the overall severity rating. A higher sub-score typically indicates a more severe or easier-to-exploit vulnerability.

CIA Impact Analysis

Below is the Impact Analysis for CVE-2026-26129, showing how Confidentiality, Integrity, and Availability might be affected if the vulnerability is exploited. Higher values usually signal greater potential damage.

  • Confidentiality: High
    Exploiting CVE-2026-26129 can result in unauthorized access to sensitive data, severely compromising data privacy.
  • Integrity: None
    CVE-2026-26129 poses no threat to data integrity.
  • Availability: None
    CVE-2026-26129 does not impact system availability.

CVE-2026-26129 References

External References

CWE Common Weakness Enumeration

CWE-138

CAPEC Common Attack Pattern Enumeration and Classification

  • HTTP Request Splitting CAPEC-105 An adversary abuses the flexibility and discrepancies in the parsing and interpretation of HTTP Request messages by different intermediary HTTP agents (e.g., load balancer, reverse proxy, web caching proxies, application firewalls, etc.) to split a single HTTP request into multiple unauthorized and malicious HTTP requests to a back-end HTTP agent (e.g., web server). See CanPrecede relationships for possible consequences.
  • Command Delimiters CAPEC-15 An attack of this type exploits a programs' vulnerabilities that allows an attacker's commands to be concatenated onto a legitimate command with the intent of targeting other resources such as the file system or database. The system that uses a filter or denylist input validation, as opposed to allowlist validation is vulnerable to an attacker who predicts delimiters (or combinations of delimiters) not present in the filter or denylist. As with other injection attacks, the attacker uses the command delimiter payload as an entry point to tunnel through the application and activate additional attacks through SQL queries, shell commands, network scanning, and so on.
  • HTTP Response Splitting CAPEC-34 An adversary manipulates and injects malicious content, in the form of secret unauthorized HTTP responses, into a single HTTP response from a vulnerable or compromised back-end HTTP agent (e.g., web server) or into an already spoofed HTTP response from an adversary controlled domain/site. See CanPrecede relationships for possible consequences.

Vulnerable Configurations

  • cpe:2.3:a:microsoft:365_copilot_chat:-:*:*:*:*:*:*:*
    cpe:2.3:a:microsoft:365_copilot_chat:-:*:*:*:*:*:*:*

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