VulnerabilityPublished 30 Dec 2025Updated 2 Jan 2026

CVE-2025-66834: server · A CSV Formula Injection

Affects serverSource CVE Database V5

Not known to be exploited · CVSS 7.3 High.

Data as of 26 Oct 2026, 17:16 UTC

CVSS 3.1 base score

7.3High

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

EPSS: 0.3% chance of exploitation in 30 days – higher than 23% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: Low
User Interaction: Required
Scope: Unchanged
Confidentiality: High
Integrity: High
Availability: None

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

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, 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: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: Required: Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 30 Dec 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
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), 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
GitHubtrueconf/server`pkg:github/trueconf/server`Other threats	Affected =5.5.2.10813	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

To mitigate CVE-2025-66834, organizations should implement input sanitization or escaping mechanisms to neutralize formula characters in Display Names before exporting to CSV. If possible, disable or restrict CSV export functionality to trusted users only. Educate employees and auditors about the risks of opening CSV files from untrusted sources and encourage the use of safer file formats or viewing methods that do not execute formulas automatically. Employ endpoint protection solutions that can detect and block malicious spreadsheet behavior. Monitor and audit exported files for suspicious content. Until an official patch is released by TrueConf, consider applying custom filters or scripts to cleanse exported CSV files before distribution. Engage with TrueConf support to obtain updates or workarounds. Finally, incorporate this vulnerability into organizational threat modeling and incident response plans to ensure rapid detection and containment if exploited.

Description

A CSV Formula Injection vulnerability in TrueConf Server v5.5.2.10813 allows a normal user to inject malicious spreadsheet formulas into exported chat logs via crafted Display Name.

Impact

For European organizations, this vulnerability could lead to significant data breaches or unauthorized actions if malicious CSV files are opened by employees or auditors. Confidential information contained in chat logs could be exfiltrated or manipulated through formula execution. Integrity of audit trails and compliance documentation may be compromised, undermining regulatory adherence such as GDPR. The attack requires user interaction but can be triggered by opening a seemingly benign exported file, increasing the risk of successful exploitation. Organizations relying on TrueConf Server for internal or external communications, especially in sectors like finance, healthcare, or government, face elevated risks. The lack of a patch and known exploits means organizations must proactively mitigate the risk. Additionally, the vulnerability could be leveraged in targeted spear-phishing campaigns within European enterprises, amplifying its impact.

CWE-1236Improper Neutralization of Formula Elements in a CSV File (opens in a new tab)
Base weakness
The product saves user-provided information into a Comma-Separated Value (CSV) file, but it does not neutralize or incorrectly neutralizes special elements that could be interpreted as a command when the file is opened by a spreadsheet product.
Implementation
When generating CSV output, ensure that formula-sensitive metacharacters are effectively escaped or removed from all data before storage in the resultant CSV. Risky characters include '=' (equal), '+' (plus), '-' (minus), and '@' (at).
Implementation
If a field starts with a formula character, prepend it with a ' (single apostrophe), which prevents Excel from executing the formula.
Architecture and Design
Certain implementations of spreadsheet software might disallow formulas from executing if the file is untrusted, or if the file is not authored by the current user.
OWASP Cheat Sheets
Abuse Case (opens in a new tab)
Deserialization (opens in a new tab)
OWASP ASVS 4.0.3
V1.5.1 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 6 Jan 2026, 22:44 UTC

WeaknessesCWE-1236

Technical details

References

Community reviews

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