CVE Intelligence
CISA KEV Critical Input validation exploit reference

CVE-2020-3161 — Cisco IP Phones Web Server Remote Code Execution and Denial-of-Service Vulnerability

A vulnerability in the web server for Cisco IP Phones could allow an unauthenticated, remote attacker to execute code with root privileges or cause a reload of an affected IP phone, resulting in a denial of service (DoS) condition. The vulnerability is due to a lack of proper input validation of HTTP requests. An attacker could exploit this vulnerability by sending a crafted HTTP request to the web server of a targeted device. A successful exploit could allow the attacker to remotely execute code with root privileges or cause a reload of an affected IP phone, resulting in a DoS condition.

Published Apr 15, 2020 · Updated Oct 13, 2026 · Sources: CISA Known Exploited Vulnerabilities, NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP, GitHub Security Advisories · CNA: cisco

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

CISA KEV · Nov 3, 2021 Exploit-DB · 1
How the score was calculated
  • Confirmed exploitation (CISA KEV)+35
  • Public exploit/PoC (exploitdb)+8
  • EPSS 83.9% (30-day exploitation probability)+15
  • Technical severity (critical)+10
  • Automatable exploitation (SSVC)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Confirmed
CISA KEV, listed Nov 3, 2021
EPSS FIRST
83.86%
ahead of 100% of scored CVEs · Oct 14, 2026
Affects
Cisco
8831 Firmware and 12 more
CVSS base
9.8
Critical · 4 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation
Active
none · proof-of-concept · active
Automatable
Yes
can an attacker script the kill-chain steps
Technical impact
Total
partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

CISA required action CISA

Apply updates per vendor instructions.

US federal deadline: May 3, 2022 — passed 1626 day(s) ago

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Cisco 8831 Firmware, Cisco Ip Phone 7811 Firmware, Cisco Ip Phone 7821 Firmware…).
  2. Treat as emergency remediation: the CVE is in CISA KEV (confirmed exploitation).
  3. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
  4. No fix documented in the sources: reduce exposure and monitor the vendor advisory.
  5. EPSS ahead of 100% of scored CVEs: prioritize it in the patch queue.
  6. Search available logs for exploit probes matching the vulnerability class (input validation), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Cisco 8831 Firmware version 11.0(5)sr1version 11.0(1)version 10.3(1)es14 Vulnerable NIST National Vulnerability Database
Cisco Ip Phone 7811 Firmware version 11.0(1) Vulnerable NIST National Vulnerability Database
Cisco Ip Phone 7821 Firmware version 11.0(1) Vulnerable NIST National Vulnerability Database
Cisco Ip Phone 7841 Firmware version 11.0(1) Vulnerable NIST National Vulnerability Database
Cisco Ip Phone 7861 Firmware version 11.0(1) Vulnerable NIST National Vulnerability Database
Cisco Ip Phone 8811 Firmware version 11.0(5)sr1version 11.0(1)version 10.3(1)es14 Vulnerable NIST National Vulnerability Database
Cisco Ip Phone 8821 Firmware version 11.0(5)sr1version 11.0(1)version 10.3(1)es14 Vulnerable NIST National Vulnerability Database
Cisco Ip Phone 8821-ex Firmware version 10.3(1)es14version 11.0(1)version 11.0(5)sr1 Vulnerable NIST National Vulnerability Database
Cisco Ip Phone 8841 Firmware version 11.0(5)sr1version 10.3(1)es14version 11.0(1) Vulnerable NIST National Vulnerability Database
Cisco Ip Phone 8845 Firmware version 11.0(1)version 11.0(5)sr1version 10.3(1)es14 Vulnerable NIST National Vulnerability Database
Cisco Ip Phone 8851 Firmware version 11.0(5)sr1version 11.0(1)version 10.3(1)es14 Vulnerable NIST National Vulnerability Database
Cisco Ip Phone 8861 Firmware version 11.0(5)sr1version 11.0(1)version 10.3(1)es14 Vulnerable NIST National Vulnerability Database
Cisco Ip Phone 8865 Firmware version 10.3(1)es14version 11.0(5)sr1version 11.0(1) Vulnerable NIST National Vulnerability Database

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
9.8 CVSS 3.1 Critical 3.9 5.9 nvd@nist.gov via NIST National Vulnerability Database
9.8 CVSS 3.1 Critical — — GitHub, Inc. via GitHub Security Advisories
9.8 CVSS 3.0 Critical 3.9 5.9 psirt@cisco.com via NIST National Vulnerability Database
9.8 CVSS 3.0 Critical — — cisco via CVE Program (cve.org) e CISA ADP
10.0 CVSS 2.0 High 10.0 10.0 nvd@nist.gov via NIST National Vulnerability Database
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H (score shown at the top: nvd@nist.gov)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-20 · Improper Input Validation

Other CVEs with this weakness →

CISA KEV details CISA

CISA lists a CVE once it has evidence of exploitation against real targets.

Listed
Nov 3, 2021
Federal deadline
May 3, 2022
passed 1626 day(s) ago
Ransomware use
Unknown

CISA records ransomware use only for campaigns it has confirmed, so “Unknown” means unrecorded, not ruled out. The deadline binds US federal agencies; for everyone else it is a reference date.

Public exploits, PoCs and detection templates

Public code that demonstrates or tests the flaw raises the odds of mass exploitation — and Nuclei templates help find vulnerable assets in your environment.

Exploit-DB

Warning: public PoCs are sometimes disguised malware. Use them only for authorized testing in an isolated environment. This portal does not host exploit code — it only points to the sources.

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 83.86%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
  • Hunt retroactively in logs from before Nov 3, 2021 (KEV listing): exploitation may have started earlier.
web/proxy/WAF logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first.

  • 2026
  • SSVC assessment updated
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 13, 2026
  • Affected products added · cisco/ip phone 8865 firmware, cisco/ip phone 8851 firmware, cisco/ip phone 7841 firmware, cisco/ip phone 7821 firmware,
    Oct 13, 2026 · NIST National Vulnerability Database
  • CVSS changed · 9.8
    Oct 13, 2026 · NIST National Vulnerability Database
  • Source status changed · → Analyzed
    Oct 13, 2026 · NIST National Vulnerability Database
  • Added to CISA KEV (detected)
    Oct 13, 2026 · CISA Known Exploited Vulnerabilities
  • Record created in this database
    Oct 13, 2026 · CISA Known Exploited Vulnerabilities
  • 2021
  • Added to CISA KEV catalog
    Nov 2, 2021 · CISA
  • 2020
  • CVE published
    Apr 15, 2020 · cisco

Source activity

Repeated readings are counted rather than listed.

  • 2× References added · Oct 13, 2026 – Oct 13, 2026
  • 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

5 on the record

Elsewhere on this site

Cisco
every CVE for this vendor
2021-11
what else CISA listed that month
Input validation
same class
CWE-20
other pages naming this weakness

Related CVEs (same products)

  • CVE-2025-20351 Cisco Desk Phone 9800 Series, IP Phone 7800 and 8800 Series, and Video Phone 8875 with SIP Firmware Cross-Site Scripting Vulnerability Oct 15, 2025
  • CVE-2025-20350 Cisco Desk Phone 9800 Series, IP Phone 7800 and 8800 Series, and Video Phone 8875 with SIP Firmware Denial of Service Vulnerability Oct 15, 2025
  • CVE-2020-26140 Use of a Broken or Risky Cryptographic Algorithm in Alfa Awus036h Firmware May 11, 2021

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No fixed version, patch or mitigation documented.
  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2020-3161 is "Cisco IP Phones Web Server Remote Code Execution and Denial-of-Service Vulnerability", rated Critical. It affects 8831 Firmware (Cisco); versions are in the scope table. It is in CISA KEV: there is evidence of real-world exploitation. CVSS 9.8 describes technical severity. EPSS 83.86% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

Comments

Moderated technical discussion. Read the community guidelines.

No comments yet.

Sign in or create an account to comment and suggest corrections.