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Yandex BrowserApplication · Yandex

CVE-2021-25263

HIGH · 7.8 CVSS v3.1 Published 2021-08-17
Fix available
A fix is available. Upgrade to 21.9.0.390 or later.
See remediation →
80/100
Remediation priority · High
Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Local privilege vulnerability in Yandex Browser for Windows prior to 21.9.0.390 allows a local, low privileged, attacker to execute arbitary code with the SYSTEM privileges through manipulating files in directory with insecure permissions during Yandex Browser update process.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Yandex Browser for Windows prior to 21.9.0.390 contains a local privilege escalation vulnerability where low-privileged users can manipulate files in a directory with insecure permissions during the browser update process to execute arbitrary code with SYSTEM privileges.

MitigationUpdate Yandex Browser to version 21.9.0.390 or later to remediate this vulnerability.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Yandex BrowserApplication
Affected:< 21.9.0.390

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check if Yandex Browser is installed
    Open File Explorer and navigate to %LOCALAPPDATA%\Yandex\YandexBrowser\Application\ or C:\Program Files\Yandex\YandexBrowser\Application\. If the folder exists, the browser is installed.
    Affected if The Yandex Browser folder exists on the system.
  2. Find the installed version number
    Locate the file 'version.ini' in the Yandex Browser Application folder and open it in a text editor, or right-click on the YandexBrowser.exe file, select Properties, and view the Details tab for the Product version.
    Affected if The version displayed is lower than 21.9.0.390.
  3. Verify version via command line
    Open Command Prompt and run: dir "%LOCALAPPDATA%\Yandex\YandexBrowser\Application\*.*" /b to list application folders, then find the version string in the folder name, or use: reg query "HKLM\SOFTWARE\Yandex\Browser" /v Version
    Affected if The command returns a version string lower than 21.9.0.390.
  4. Confirm update service configuration
    Open Services (services.msc) and locate the Yandex Update service. Check if it exists and its startup type. Also verify directory permissions on %LOCALAPPDATA%\Yandex\YandexBrowser\Application\ by right-clicking the folder, selecting Properties, then Security tab.
    Affected if The Yandex Update service is present and the application folder permissions allow modification by low-privileged users.

If Yandex Browser for Windows is installed with a version lower than 21.9.0.390, the system is affected by this privilege escalation vulnerability.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 21.9.0.390 or later
Fixed in 21.9.0.390
Interim mitigation

Update Yandex Browser to version 21.9.0.390 or later to remediate this vulnerability.

Recommended fix High confidence

Yandex Browser 21.9.0.390 or later

  1. 1. Ensure you have administrator privileges on the Windows machine
  2. 2. Open Yandex Browser and navigate to the menu (three dots) > Help > About Yandex Browser
  3. 3. If an update is available, click 'Update' to download and install version 21.9.0.390 or later
  4. 4. Alternatively, download the latest version of Yandex Browser from the official website at https://browser.yandex.com
  5. 5. Run the installer with administrator privileges to update the browser
  6. 6. Restart the browser after the update completes
  7. 7. Verify the updated version by going to Help > About Yandex Browser and confirming the version is 21.9.0.390 or higher
Caveat Standard browser update - ensure any local extensions or settings are compatible with the new version

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Yandex Browser Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,240
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,984.

Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-25263 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data