# CVE-2026-20281: Denial of service in Cisco Session Initiation Protocol (SIP) Software

> Remote attackers can cause denial of service on Cisco IP phones by sending crafted HTTP packets, requiring Web Access to be enabled.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 2 Sep 2026
- **Updated:** 2 Sep 2026
- **Also known as:** GHSA-998p-wvfv-584p

## What is CVE-2026-20281?

CVE-2026-20281 is a high-severity denial of service vulnerability in Cisco Session Initiation Protocol (SIP) Software, published on 2 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-401 (Missing Release of Memory after Effective Lifetime)

## Which versions are affected by CVE-2026-20281?


## How do I fix CVE-2026-20281?

No fix has been published for CVE-2026-20281 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-20281 being exploited?

There is no known exploitation of CVE-2026-20281 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-20281 and fix it if it is affected.

What it is: CVE-2026-20281 is a high-severity denial of service vulnerability in Cisco Session Initiation Protocol (SIP) Software, published on 2 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-20281 in the wild and no public exploit code.

Affected product: Cisco Session Initiation Protocol (SIP) Software. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-20281/ (Markdown: https://insights.sbomify.com/CVE-2026-20281/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-20281
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-20281
- OSV: https://osv.dev/vulnerability/CVE-2026-20281

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-20281/
Summaries are generated and may contain mistakes; the official description above is the record.