Desk Phone 9841 FirmwareOperating system · Cisco
CVE-2025-20335
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 · uneditedA vulnerability in the directory permissions of Cisco Desk Phone 9800 Series, Cisco IP Phone 7800 and 8800 Series, and Cisco Video Phone 8875 could allow an unauthenticated, remote attacker to write arbitrary files on an affected device. This vulnerability is due to a lack of proper authentication controls. An attacker could exploit this vulnerability by sending a crafted request to an affected device. A successful exploit could allow the attacker to perform arbitrary file writes to specific directories in the underlying operating system. Note: To exploit this vulnerability, Web Access must be enabled on the phone. Web Access is disabled by default.
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 confidenceThis is an authentication bypass vulnerability in Cisco IP phones where improper directory permissions allow unauthenticated remote attackers to write arbitrary files to specific directories on the device via crafted HTTP requests. The vulnerability exists in the web server component and requires Web Access to be enabled (disabled by default).
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
Desk Phone 9841 FirmwareOperating system
>= 3.0\(1\), < 3.3\(1\)
Desk Phone 9851 FirmwareOperating system
>= 3.0\(1\), < 3.3\(1\)
Desk Phone 9861 FirmwareOperating system
>= 3.0\(1\), < 3.3\(1\)
Desk Phone 9871 FirmwareOperating system
>= 3.0\(1\), < 3.3\(1\)
Ip Phone 7811 FirmwareOperating system
< 14.3\(1\)= 14.3\(1\)
Ip Phone 7821 FirmwareOperating system
< 14.3\(1\)= 14.3\(1\)
Ip Phone 7841 FirmwareOperating system
< 14.3\(1\)= 14.3\(1\)
Ip Phone 7861 FirmwareOperating system
< 14.3\(1\)= 14.3\(1\)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
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
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 checksWork through these to decide whether this CVE applies to you.
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Identify the phone modelLocate the model number on the phone label, the phone screen, or the Cisco administration web interface. Confirm it is one of: Cisco Desk Phone 9841, 9851, 9861, 9871, or Cisco IP Phone 7811, 7821, 7841, 7861.Affected if The phone model is not one of the eight affected models listed.
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Check the installed firmware versionAccess the phone administration interface, go to the Device Information or Status page, and record the Firmware Version. Alternatively, press the Applications or Settings button on the phone and navigate to Device Information to view the software version.Affected if The firmware version is 3.0(1) or higher but lower than 3.3(1) for Desk Phone models 9841/9851/9861/9871; OR the firmware version is 14.3(1) or any version lower than 14.3(1) for IP Phone models 7811/7821/7841/7861.
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Verify if Web Access is enabledLog into the Cisco phone administration web interface and navigate to the Administration or Network settings section. Locate the Web Access or HTTP Server setting and determine whether it is set to Enabled or Disabled.Affected if Web Access is set to Enabled. If Web Access is Disabled (the default setting), the vulnerability is not exploitable in this environment.
Your phone is affected if it is an affected model, runs a firmware version within the vulnerable range, AND has Web Access enabled.
Generated from the published advisory. Verify against your own configuration.
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 · scoped3.314.3
Disable Web Access on affected phones if not business-critical; if required, apply Cisco firmware updates when available and restrict access to trusted networks only.
Desk Phone 9800 Series: firmware >= 3.3(1); IP Phone 7800/8800 Series: firmware >= 14.4(1)
- 1. Identify all affected Cisco Desk Phone and IP Phone devices in your inventory using the model and firmware versions provided.
- 2. Obtain the latest Cisco firmware release for your specific phone model from the Cisco Software Download center or official Cisco documentation.
- 3. For Desk Phone 9841/9851/9861/9871: Upgrade to firmware version 3.3(1) or later.
- 4. For IP Phone 7811/7821/7841/7861: Upgrade to firmware version 14.4(1) or later.
- 5. After upgrading, verify that Web Access is disabled on the phones if not required for business operations, as the vulnerability requires Web Access to be enabled.
- 6. Confirm the vulnerability is remediated by verifying the new firmware version is installed and testing that unauthenticated file write is no longer possible.
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Desk Phone 9841 Firmware
Scoped from the published advisory
- Consultation3.0 h
- Implementation6.0 h
- Testing3.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,984.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2025-20335 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2025-20335 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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