The vulnerability identified as CVE-2025-21088 affects multiple versions of Mattermost, specifically versions 10.2.x up to 10.2.0, 9.11.x up to 9.11.5, 10.0.x up to 10.0.3, and 10.1.x up to 10.1.3. This vulnerability allows attackers to exploit the system by providing crafted malicious input that can crash the frontend application.
With a CVSS score of 6.5, the severity of this vulnerability is classified as medium, indicating a significant risk to organizations using affected versions of Mattermost. The potential for disruption is particularly concerning, as the availability impact is rated as high.
Organizations utilizing Mattermost should prioritize patching immediately to mitigate the risks associated with this vulnerability. The potential for attackers to leverage this weakness to affect service availability poses a real threat.
Currently, there are no known exploits or public proof of concepts associated with this vulnerability, which suggests that while the risk is present, it may not yet be actively exploited in the wild.
Vulnerability Details
According to the official CVE description, Mattermost fails to validate the style of proto supplied to an action's style in post.props.attachments. This oversight can lead to the crashing of the frontend when maliciously crafted inputs are processed.
The CVSS vector string for this vulnerability is CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H. The breakdown indicates that the attack vector is network-based, with low complexity and low privileges required to exploit, while user interaction is not necessary. The availability impact is high, which makes this vulnerability particularly concerning for organizations.
Technical Analysis
The root cause of this vulnerability lies in the improper validation of input data concerning the style property in post attachments. This lack of validation results in the application being susceptible to crashes when it encounters unexpected input formats.
The attack vector is network-based, enabling attackers to remotely send crafted data to the Mattermost server without needing any local access or user interaction. The complexity of executing this attack is categorized as low, indicating that even less sophisticated attackers may exploit this vulnerability. The requirement for only low privileges means that an attacker could potentially leverage this vulnerability without extensive permissions within the application.
In terms of impacts, this vulnerability does not affect confidentiality or integrity, but it significantly compromises availability. Organizations may experience downtime or service interruptions due to application crashes caused by this vulnerability.
Risk & Impact Analysis
The real-world risk associated with CVE-2025-21088 is significant for organizations using vulnerable versions of Mattermost. The potential impact on service availability necessitates immediate action from organizations to patch the affected versions.
The blast radius of this vulnerability can be considerable, especially in environments where Mattermost is utilized for critical communications or operational workflows. Organizations need to assess their use of Mattermost and the impact that a downtime event could have on their operations.
Given the medium severity rating and the high availability impact, organizations should address this vulnerability in their priority patch cycle to minimize the risk of disruption.
Exploitation Status
Signal | Status |
|---|---|
Known Exploit | No |
Public PoC | No |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
Affected versions of Mattermost include:
• Mattermost versions 10.2.x up to 10.2.0 • Mattermost versions 9.11.x up to 9.11.5 • Mattermost versions 10.0.x up to 10.0.3 • Mattermost versions 10.1.x up to 10.1.3
Mitigation & Remediation
Organizations should prioritize updating to the latest version of Mattermost to remediate this vulnerability. Ensure that all instances of Mattermost Server are upgraded beyond the affected versions listed above.
In the absence of a patch, organizations may consider implementing input validation controls to filter and sanitize inputs to prevent exploitation of the vulnerability until a remediation can be applied.
For further guidance on security testing, organizations may reference resources on penetration testing and application security assessments.
Detection Guidance
To detect potential exploitation of this vulnerability, organizations should monitor logs for unusual frontend crashes or error messages related to post attachments.
Behavioral anomalies in user interactions, particularly when posting attachments, should also be analyzed to identify potential attempts to exploit this vulnerability.
AppSecure Threat Intelligence Insight
While CVE-2025-21088 is currently not actively exploited, its potential for causing significant disruption highlights the importance of maintaining robust application security practices.
Organizations should consider adopting a comprehensive vulnerability management program to regularly assess and remediate vulnerabilities. For more insights on building effective programs, organizations can refer to the vulnerability management program design.
Moreover, organizations should stay informed about potential trends in vulnerabilities and threats. The ongoing analysis of vulnerabilities like CVE-2025-21088 can provide valuable learning opportunities. For more information on vulnerability exposure trends, organizations can explore resources such as the 2025 vulnerability exposure severity trends.
Overall, organizations should adopt a proactive stance on security, ensuring they are prepared to respond effectively to vulnerabilities as they emerge.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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