---
id: "CVE-2026-106804"
kind: "vulnerability"
aliases: ["CVE-2026-106804"]
title: "Kamailio: stack buffer overflow in ims_qos_npn lets crafted SIP REGISTER crash server"
severity: "high"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: [{"name": "kamailio", "fixed": ["6.1.5"], "affected": "6.1.3, 6.1.4 (ims_qos_npn module)", "ecosystem": "vendor"}]
ecosystems: []
tags: ["ims", "kamailio", "runtime", "self-hosted", "sip", "voip"]
not_affected_if: ["fixed-6.1.5", "ims-qos-npn-not-loaded", "other-kamailio-versions"]
published_at: "2026-11-02T17:17:33+00:00"
first_seen_at: "2026-11-02T17:24:12+00:00"
updated_at: "2026-11-02T17:27:49+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-106804", "first_seen_at": "2026-11-02T17:24:12+00:00"}, {"source": "analyst", "url": null, "first_seen_at": "2026-11-02T17:27:49+00:00"}]
---

# Kamailio: stack buffer overflow in ims_qos_npn lets crafted SIP REGISTER crash server

Kamailio versions 6.1.3 and 6.1.4 copy the host field from a SIP Via header into a fixed 46-byte stack buffer in the ims_qos_npn module without a length check. An unauthenticated remote attacker can send a crafted SIP REGISTER request to corrupt the stack and crash the Kamailio process, causing denial of service.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:kamailio affected 6.1.3, 6.1.4 (ims_qos_npn module) fixed 6.1.5

## How to check

1. Run `kamailio -v`: 6.1.3 and 6.1.4 are reported affected; 6.1.5 has the fix. Distro packages may backport, so check the package changelog for 'ims_qos_npn: check Via host length'.
2. Grep your config for `loadmodule "ims_qos_npn"` and for `Rx_AAR_Register`. The reporter says the vulnerable code runs on each REGISTER when Rx_AAR_Register() is called; if the module is not loaded, this issue does not apply.
3. Also check if you run an older 6.0.x/5.x build that includes ims_qos_npn (added in PR #3921, 2024): the reporter tested only 6.1.3 and checked 6.1.4 and master by source reading; earlier versions are unconfirmed.

## Fix

Upgrade Kamailio to 6.1.5 (released 2026-10-15), which includes the ims_qos_npn Via host length check (commit 41326b65, backport of master fb93ca8c, fixes issue #4953). Building from master after 2026-09-28 also has it.

## Timeline

- 2026-11-02T17:24:12+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-106804
- 2026-11-02T17:27:49+00:00 analyst — Fixed upstream: master fb93ca8c (2026-09-28), 6.1 branch 41326b65 (2026-10-13), shipped in 6.1.5 ChangeLog. Reporter issue #4953 gives details; no exploitation or public PoC code seen. Default-load state: module is optional, not shown as default; not verified against default cfg. Older versions unconfirmed.

## Documents

- [advisory] git:master:fb93ca8c: ims_qos_npn: check Via host length before copying (Fixes #4953) https://kamailio.org/mailman3/hyperkitty/list/sr-dev@lists.kamailio.org/thread/GZUT2MHPIOGBK4XMBLSCHCVS77FK7MMW/
- [advisory] Issue #4953: ims_qos_npn missing Via host length check in w_rx_aar_register() https://kamailio.org/mailman3/hyperkitty/list/sr-dev@lists.kamailio.org/message/IYWLBMEAABC3JOBR2DUNUBL2LVFLYPCF/attachment/2/attachment.html
- [fix] Kamailio 6.1.5 ChangeLog (includes ims_qos_npn Via host length check) https://www.kamailio.org/pub/kamailio/6.1.5/ChangeLog
- [fix] Kamailio v6.1.5 Released https://www.kamailio.org/w/2026/10/kamailio-v6-1-5-released/

## From the sources

A stack-based buffer overflow exists in Kamailio v6.1.3 and v6.1.4 in the ims_qos_npn module. The w_rx_aar_register() function copies the attacker-controlled host field from the SIP `Via` header into a fixed 46-byte stack buffer without validating its length. An unauthenticated remote attacker can trigger the vulnerability with a crafted SIP `REGISTER` request, causing stack corruption and termination of the affected Kamailio instance, resulting in denial of service.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_