Cisco Desk Phone SIP HTTP DoS via memory exhaustion
CVE-2026-20281 Published on September 2, 2026
Cisco Desk Phone 9800 Series, IP Phone 7800 and 8800 Series, and Video Phone 8875 with SIP Software Denial of Service Vulnerability
A vulnerability in Cisco Desk Phone 9800 Series, Cisco IP Phone 7800 and 8800 Series, and Cisco Video Phone 8875 that are running Cisco Session Initiation Protocol (SIP) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device.
This vulnerability is due to improper memory management when an affected device processes HTTP packets. An attacker could exploit this vulnerability by sending a continuous stream of crafted HTTP packets to the device. A successful exploit could allow the attacker to cause the affected device to continuously consume memory, resulting in a DoS condition. A manual reboot of the device is required to recover from this condition.
Note: For this vulnerability to be exploitable, the phone must be registered to Cisco Unified Communications Manager (Unified CM) and have Web Access enabled. Web Access is disabled by default.
Vulnerability Analysis
CVE-2026-20281 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a high impact on availability.
Weakness Type
What is a Memory Leak Vulnerability?
The software does not sufficiently track and release allocated memory after it has been used, which slowly consumes remaining memory. This is often triggered by improper handling of malformed data or unexpectedly interrupted sessions. In some languages, developers are responsible for tracking memory allocation and releasing the memory. If there are no more pointers or references to the memory, then it can no longer be tracked and identified for release.
CVE-2026-20281 has been classified to as a Memory Leak vulnerability or weakness.
Affected Versions
Cisco Session Initiation Protocol (SIP) Software:- Version 12.1(1)SR1 is affected.
- Version 11.5(1) is affected.
- Version 10.3(2) is affected.
- Version 10.2(2) is affected.
- Version 10.3(1) is affected.
- Version 10.3(1)SR4 is affected.
- Version 11.0(1) is affected.
- Version 10.4(1)SR2 3rd Party is affected.
- Version 11.7(1) is affected.
- Version 12.1(1) is affected.
- Version 11.0(0.7) MPP is affected.
- Version 9.3(4) 3rd Party is affected.
- Version 12.5(1)SR2 is affected.
- Version 10.2(1)SR1 is affected.
- Version 9.3(4)SR3 3rd Party is affected.
- Version 10.2(1) is affected.
- Version 12.5(1) is affected.
- Version 10.3(1)SR2 is affected.
- Version 11-0-1MSR1-1 is affected.
- Version 10.4(1) 3rd Party is affected.
- Version 12.5(1)SR1 is affected.
- Version 11.5(1)SR1 is affected.
- Version 10.1(1)SR2 is affected.
- Version 12.0(1)SR2 is affected.
- Version 12.6(1) is affected.
- Version 10.3(1.11) 3rd Party is affected.
- Version 12.0(1) is affected.
- Version 12.0(1)SR1 is affected.
- Version 9.3(3) is affected.
- Version 12.5(1)SR3 is affected.
- Version 10.3(1)SR4b is affected.
- Version 9.3(4)SR1 3rd Party is affected.
- Version 10.3(1)SR5 is affected.
- Version 10.1(1.9) is affected.
- Version 10.3(1.9) 3rd Party is affected.
- Version 9.3(4)SR2 3rd Party is affected.
- Version 10.3(1)SR1 is affected.
- Version 10.3(1)SR3 is affected.
- Version 10.1(1)SR1 is affected.
- Version 12.0(1)SR3 is affected.
- Version 12.6(1)SR1 is affected.
- Version 12.7(1) is affected.
- Version 10.3(1)SR6 is affected.
- Version 12.8(1) is affected.
- Version 12.7(1)SR1 is affected.
- Version 11.0(2)SR1 is affected.
- Version 11.0(4) is affected.
- Version 11.0(2) is affected.
- Version 11.0(4)SR3 is affected.
- Version 11.0(5) is affected.
- Version 11.0(3)SR2 is affected.
- Version 11.0(3)SR4 is affected.
- Version 11.0(3)SR3 is affected.
- Version 11.0(2)SR2 is affected.
- Version 11.0(4)SR1 is affected.
- Version 11.0(5)SR3 is affected.
- Version 11.0(3) is affected.
- Version 11.0(5)SR2 is affected.
- Version 11.0(3)SR6 is affected.
- Version 11.0(5)SR1 is affected.
- Version 11.0(4)SR2 is affected.
- Version 11.0(3)SR1 is affected.
- Version 11.0(3)SR5 is affected.
- Version 11.0(6) is affected.
- Version 12.8(1)SR1 is affected.
- Version 12.8(1)SR2 is affected.
- Version 14.0(1) is affected.
- Version 14.0(1)SR1 is affected.
- Version 11.0(6)SR1 is affected.
- Version 10.3(1)SR7 is affected.
- Version 14.0(1)SR2 is affected.
- Version 14.1(1) is affected.
- Version 14.0(1)SR3 is affected.
- Version 11.0(6)SR2 is affected.
- Version 14.1(1)SR1 is affected.
- Version 14.1(1)SR2 is affected.
- Version 11.0(6)SR4 is affected.
- Version 14.2(1) is affected.
- Version 14.2(1)SR1 is affected.
- Version 11.0(6)SR5 is affected.
- Version 14.1(1)SR3 is affected.
- Version 14.2(1)SR2 is affected.
- Version 3.1(1) is affected.
- Version 3.0(1) is affected.
- Version 2.3(1) is affected.
- Version 2.3(1)SR1 is affected.
- Version 2.2(1) is affected.
- Version 2.1(1) is affected.
- Version 2.0(1) is affected.
- Version 14.2(1)SR3 is affected.
- Version 3.1(1)SR1 is affected.
- Version 14.3(1) is affected.
- Version 3.2(1) is affected.
- Version 14.3(1)SR1 is affected.
- Version 14.2(1)SR4 is affected.
- Version 3.3(1) is affected.
- Version 11.0(6)SR6 is affected.
- Version 14.3(1)SR2 is affected.
- Version 3.4(1) is affected.
- Version 14.3(1)SR3 is affected.
- Version 3.5(1) is affected.
- Version 11.0(6)SR7 is affected.
- Version 3.5(1)SR1 is affected.
- Version 14.4(1) is affected.
- Version 3.6(1) is affected.
- Version 4.0(1) is affected.
- Version 14.4(1)SR1 is affected.
- Version 4.1(1) is affected.
- Version 14.4(1)SR2 is affected.
- Version 4.1(1)SR1 is affected.