CriticalCVE-2026-3502

    TrueConf Client Update Integrity Verification Bypass (CVE-2026-3502)

    Published In CISA KEV since Sources: CVE.org

    What is affected, what to do

    TrueConf Client downloads application update code and applies it without performing verification. An attacker who is able to influence the update delivery path can substitute a tampered update payload.

    The vulnerability is being actively exploited; treat it as a priority. Update trueconf to version 8.5.3.884. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • TrueConf Client eq TrueConf Client versions 8.1.0 through 8.5.2..TrueConf Client versions 8.1.0 through 8.5.2

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    7.8

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v3

    7.8

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: CVE.org

    5.9 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 93.2

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    224.12 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    actively exploitedSource: VulnCheck KEV (opens in a new tab) How we classify
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

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    7.8 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

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    7.8
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

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    5.9 %
    Moderate — model estimates 1-10% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

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    93.2
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

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    Actively exploited
    Published
    In CISA KEV since

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    CISA assessment (SSVC)
    Exploitation: active · not automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 31 March 2026
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-494

    Response and mitigation

    Why act now?

    Prioritisation rationale

    Exploitation requires the attacker to control the update delivery path. That means an adjacent-network position, a compromised TrueConf Server or mirror with admin rights, and a user-triggered update. Broad opportunistic scanning is therefore unlikely, and overall exploitation likelihood is rated low. The KEV listing points to targeted, supply-chain-style operations against organisations that self-host TrueConf for video conferencing, typically government, public administration and other confidentiality-sensitive operators. CISA does not flag ransomware use. Given the scope change and the high confidentiality and integrity impact, treat this as high priority and patch within days if you run TrueConf, especially with an on-prem server or in flat or shared network segments. If TrueConf is absent, an inventory check is sufficient.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Inventory: Identify every endpoint running TrueConf Client 8.1.0 through 8.5.2 (software inventory, SCCM/Intune, EDR asset query for "TrueConf"). Include meeting-room PCs, kiosks and thin clients.
      • Patch: Upgrade to TrueConf Client 8.5.3.884. Do not obtain the package through the vulnerable in-client updater. Download it directly from the vendor, verify the Authenticode signature and hash, and push it through your software distribution tooling.
      • Disable auto-update until rollout completes: Turn off the client's self-update via configuration or policy. If that is not possible, block client-initiated update downloads at the proxy until the patched build is deployed.
      • Validate the delivery path: If you run your own TrueConf Server or an internal update mirror, verify the hosted client packages against the vendor originals. Review admin accounts and logins (the vector requires high privileges) and rotate admin credentials.
      • Retro-hunt: For clients that have taken updates since 8.1.0, review recent updater executions and newly written binaries for missing or foreign signatures (see Detection rules).

    2. Runbook step 2

      Mitigation layers

      • Network, layer 2/3: The attack works from an adjacent network position (tampering with the delivery path via ARP spoofing, rogue DHCP or DNS manipulation). Enable Dynamic ARP Inspection, DHCP Snooping and IP Source Guard on access switches. Enforce 802.1X and keep guest/BYOD segments strictly separated from workstation VLANs.
      • Network, egress: Force TrueConf client update traffic through the authenticating proxy and restrict it to approved vendor destinations or your own TrueConf Server. Block cleartext HTTP downloads of executables by TrueConf processes.
      • Endpoint hardening: Enforce a WDAC or AppLocker publisher rule that allows only vendor-signed binaries and MSIs to execute from the TrueConf install and temp directories, and blocks unsigned ones. Enable the ASR rule "Block executable files unless they meet a prevalence, age, or trusted list criterion".
      • IAM / least privilege: Run end users without local admin rights so a tampered update cannot run elevated. Restrict TrueConf Server admin roles to named individuals, require MFA, and allow admin access only via a jump host.
      • Configuration: Permanently move client updates to centrally managed distribution with hash and signature validation before release, rather than relying on client self-update. Keep this as defence in depth even after patching.

    3. Runbook step 3

      Detection rules

      • EDR/Sysmon process ancestry (Sysmon EID 1 / Security 4688): A TrueConf process or its updater spawns shells or LOLBins. KQL: DeviceProcessEvents | where InitiatingProcessFolderPath has "TrueConf" and FileName in~ ("cmd.exe","powershell.exe","pwsh.exe","rundll32.exe","regsvr32.exe","mshta.exe","wscript.exe")
      • Unsigned update artefacts (Sysmon EID 11 / EID 7): A TrueConf process writes .exe, .dll or .msi files that are unsigned or not signed by the vendor, or unsigned DLLs are loaded into TrueConf processes. KQL: DeviceFileEvents | where InitiatingProcessFolderPath has "TrueConf" and FileName endswith_cs ".exe", then join to DeviceFileCertificateInfo and filter on IsSigned == false or an unexpected signer.
      • Post-update persistence (Sysmon EID 12/13, Security 4698, System 7045): New Run keys, scheduled tasks or services created shortly after a TrueConf update. Sigma shape: parent|contains: TrueConf AND EventID in (4698, 7045).
      • Network telemetry (Zeek/Suricata): In Zeek http.log and files.log, look for executable MIME types fetched by TrueConf clients over cleartext HTTP or from unexpected hosts. Correlate with Zeek or arpwatch alerts for gateway ARP flapping, duplicate MAC/IP bindings, or rogue DHCP servers in the same segment.
      • TrueConf Server logs: Match unexpected admin logins and changes to hosted client packages or update settings against change tickets.

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    TrueConf Client downloads application update code and applies it without performing verification. An attacker who is able to influence the update delivery path can substitute a tampered update payload. If the payload is executed or installed by the updater, this may result in arbitrary code execution in the context of the updating process or user.

    Source: cvelistv5, NVD (NIST), CISA KEV Catalog, CVE.org (MITRE)

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    TrueConfTrueConf Client
    • TrueConf Client versions 8.1.0 through 8.5.2
    • —
    trueconftrueconf
    • < 8.5.3.884
    • 8.5.3.884

    Vendors and products

    Weakness classes (CWE)

    • CWE-494Download of Code Without Integrity Check

      Base

      The product downloads source code or an executable from a remote location and executes the code without sufficiently verifying the origin and integrity of the code.

      Entry at MITRE CWE-494

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited

    References & sources

    • trueconf.comblog/update/trueconf-8-5Product, Release notes
    • research.checkpoint.com2026/operation-truechaos-0-day-exploitation-against-southeast-a…Third-party advisory, Third-party advisory
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2026-3502government-resource, US government resource

    Linked advisories

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