VulnerabilityPublished 11 Sep 2025

CVE-2025-10255: Ascensio System SIA OnlyOffice · Cross-site Scripting

Affects Ascensio System SIA OnlyOfficeSource CVE Database V5

Public exploit available · CVSS 5.1 Medium.

Data as of 26 Oct 2026, 17:16 UTC

CVSS 4.0 base score

5.1Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.3% chance of exploitation in 30 days – higher than 25% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P

Base metrics

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: Low
User Interaction: Passive
Vulnerable system confidentiality: None
Vulnerable system integrity: Low
Vulnerable system availability: None
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Threat metrics

Exploit Maturity: POC

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: Low: The attacker requires privileges that provide basic capabilities that are typically limited to settings and resources owned by a single low-privileged user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources.
User Interaction: Passive: Successful exploitation of this vulnerability requires limited interaction by the targeted user with the vulnerable system and the attacker’s payload. These interactions would be considered involuntary and do not require that the user actively subvert protections built into the vulnerable system.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact to the Vulnerable System.
Vulnerable system availability: None: There is no impact to availability within the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.
Exploit Maturity: POC: Based on threat intelligence sources each of the following must apply: · Proof-of-concept is publicly available · No knowledge of reported attempts to exploit this vulnerability · No knowledge of publicly available solutions used to simplify attempts to exploit the vulnerability

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 11 Sep 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: evidence found.
CVSS exploit maturity: proof of concept public
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), CVSS vector, the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
Ascensio System SIA OnlyOffice	Affected 12.0 – 12.7.0 8 affected builds	Fixed in–

AI-suggested

Organizations should immediately review their OnlyOffice deployments to identify if affected versions (12.0 to 12.7.0) are in use. Until a vendor patch is released, practical mitigations include: 1) Implementing strict Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts in browsers accessing OnlyOffice; 2) Applying input validation and output encoding at the application or web server level if customization is possible; 3) Restricting access to the OnlyOffice project messaging component to trusted users and networks, ideally behind VPNs or internal networks; 4) Educating users about the risks of clicking on suspicious links or messages within OnlyOffice; 5) Monitoring web server logs for unusual requests targeting the Messages.aspx endpoint; 6) Preparing for rapid patch deployment once the vendor releases an update. Additionally, organizations should consider deploying web application firewalls (WAFs) with rules to detect and block typical XSS payloads targeting OnlyOffice components.

Description

A vulnerability was determined in Ascensio System SIA OnlyOffice up to 12.7.0. Impacted is an unknown function of the file /Products/Projects/Messages.aspx of the component Comment Handler. Executing manipulation can lead to cross site scripting. The attack may be launched remotely. The exploit has been publicly disclosed and may be utilized. The vendor was informed early about this issue and replied: "We are already working on this case, and the issues will be resolved in one of the upcoming patches."

Impact

For European organizations, the impact of this vulnerability can be significant, especially for those relying on OnlyOffice for collaborative document editing and project management. Successful exploitation could allow attackers to execute arbitrary scripts in users' browsers, potentially leading to session hijacking, theft of sensitive information, or spreading malware within the organization. This could disrupt business operations, damage reputation, and lead to compliance issues under regulations like GDPR if personal data is compromised. Since OnlyOffice is used by enterprises, educational institutions, and government agencies, the risk extends to critical sectors. The remote exploitation capability without authentication increases the attack surface, particularly in environments where OnlyOffice is exposed to the internet or accessible by multiple users. The need for user interaction somewhat limits automated exploitation but does not eliminate risk, especially in phishing or social engineering scenarios.

Summary

CVE-2025-10255 is a cross-site scripting (XSS) vulnerability identified in Ascensio System SIA's OnlyOffice product, specifically affecting versions 12.0 through 12.7.0. The vulnerability resides in an unspecified function within the /Products/Projects/Messages.aspx file, part of the Comment Handler component. This flaw allows an attacker to inject malicious scripts that execute in the context of the victim's browser when interacting with the affected component. The vulnerability can be exploited remotely without requiring authentication, although user interaction is necessary to trigger the malicious payload. The CVSS 4.0 base score is 5.1, indicating a medium severity level. The attack vector is network-based with low attack complexity and no privileges required, but user interaction is needed. The impact primarily affects the integrity of the victim's session and potentially confidentiality if sensitive data is accessible via the injected script. The vulnerability's exploitation could lead to session hijacking, defacement, or redirection to malicious sites, impacting users of OnlyOffice's project messaging functionality.

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 11 Sep 2025, 16:13 UTC

Technical details

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