CVE-2026-108822

Executive Summary

CVE-2026-108822 is a buffer overflow vulnerability in the Kamailio open-source SIP server, specifically within the isup_get_calling_party function of the sipt module (src/modules/sipt/ss7_parser.c). An unauthenticated, remote attacker can trigger the flaw by manipulating the length argument, potentially causing a denial of service (crash or instability) of the SIP service. The vulnerability affects Kamailio versions up to and including 6.0.7 and 6.1.3; upgrading to 6.0.8 or 6.1.4 resolves the issue.

Technical Analysis

The vulnerability resides in the sipt module, which handles SIP-I / SIP-T (ISUP encapsulation over SIP) signaling. The affected component processes ISUP (ISDN User Part) messages carried within SIP requests. The function isup_get_calling_party is responsible for extracting the calling party number from an incoming ISUP message body.

According to the NVD description, the flaw is caused by improper validation of the length argument. An attacker can supply a crafted ISUP message with a length field that exceeds the allocated buffer bounds, leading to a buffer overflow (CWE-119). This overflow occurs during parsing of the calling party information element. Successful exploitation depends on the exact memory layout and compiler protections, but in the best case for an attacker it leads to a crash (denial of service), and under specific conditions could potentially lead to remote code execution — though the CVSS vector (C:N/I:N/A:L) indicates only low availability impact and no confidentiality or integrity impact is expected from this vulnerability.

The attack surface is the SIP signaling interface. Kamailio typically listens on UDP/TCP port 5060 (and 5061 for TLS). The sipt module must be loaded and configured to process ISUP messages, which is common in telecom interconnect scenarios (e.g., SIP-I trunks). The attacker does not need authentication; a single crafted SIP message containing a malformed ISUP body is sufficient to trigger the vulnerable code path.

The root cause is a missing or insufficient bounds check before copying the calling party digits into a fixed-size buffer. The length argument, likely derived from the ISUP parameter length field, is trusted without verifying it against the destination buffer size. This is a classic stack or heap overflow (CWE-119).

No public proof-of-concept exists, and no exploit code is available as of this report. The patch commit (3667bebf8d0bea07ed16218fd921d07db87aeb21) likely adds a length validation check before the memory copy.

Exploitation Scenarios

1) Reconnaissance/target identification: An attacker scans for exposed Kamailio SIP servers on UDP/TCP 5060 or 5061. Shodan dorks such as product:"Kamailio" or port:5060 can identify internet-facing instances. The attacker then verifies that the target responds to SIP OPTIONS or INVITE messages and that the sipt module is active (e.g., by observing SIP-I headers in responses).

2) Triggering the flaw: The attacker crafts a SIP request (e.g., INVITE or MESSAGE) containing an ISUP message body. Within that ISUP body, the calling party number parameter is malformed: the length field is set to a value larger than the buffer intended to hold the calling party digits. When Kamailio processes this message, the isup_get_calling_party function reads the length value and attempts to copy that many bytes into a fixed-size buffer, causing an overflow.

3) Payload/execution method: At the vulnerability-class level, this is a buffer overflow. The attacker's overflow data overwrites adjacent memory on the stack or heap. Depending on the exact layout and protections (ASLR, stack canaries, DEP), the immediate effect is typically a crash (availability loss). A skilled attacker might attempt to achieve code execution by overwriting a return address or function pointer, but the CVSS vector suggests only low availability impact, implying that code execution is unlikely or unproven. No public exploit code exists, so the precise exploitation technique is not documented.

4) Post-exploitation impact: If the overflow only causes a crash, the impact is denial of service: the SIP service terminates, disrupting voice calls and signaling for all users on that Kamailio instance. If code execution were achieved (unlikely per CVSS), the attacker could gain control of the Kamailio process, potentially intercepting or manipulating SIP traffic, but this is speculative and not supported by the CVSS metrics.

Impact Assessment

The CVSS 3.1 score is 5.3 (Medium), with vector AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L. This indicates:

• Attack Vector (Network): Exploitable remotely over the network.
• Attack Complexity (Low): No special conditions required; the attacker only needs to send a crafted packet.
• Privileges Required (None): No authentication needed.
• User Interaction (None): No victim action required.
• Scope (Unchanged): The impact is confined to the vulnerable component.
• Confidentiality (None): No data exposure expected.
• Integrity (None): No data modification expected.
• Availability (Low): The vulnerability can cause a partial or temporary disruption of service, such as a crash that may be automatically restarted.

Business impact: Kamailio is widely used in VoIP and telecom infrastructure (SIP proxies, session border controllers, IMS). A successful exploit can disrupt voice services, leading to dropped calls, failed emergency calls, and revenue loss for service providers. The blast radius includes all users relying on the affected Kamailio instance for call routing. Because the attack is unauthenticated and remote, any internet-exposed Kamailio with the sipt module enabled is at risk.

Detection Guidance

Sigma Rule

title: Kamailio SIPT Buffer Overflow Attempt (CVE-2026-108822)
id: 6a1b2c3d-4e5f-6a7b-8c9d-0e1f2a3b4c5d
status: experimental
description: Detects malformed ISUP messages targeting the isup_get_calling_party function in Kamailio sipt module.
author: Valters IT
date: 2026-01-01
logsource:
  product: kamailio
  service: sipt
detection:
  selection:
    event_type: 'sipt_parse_error'
    error_message|contains: 'isup_get_calling_party'
  condition: selection
falsepositives:
  - Legitimate malformed ISUP messages from misconfigured peers
level: medium
tags:
  - attack.t1190
  - cve.2026.108822

YARA Rule

rule CVE_2026_108822_Kamailio_SIPT_Overflow
{
    meta:
        description = "Detects crafted ISUP messages attempting to exploit CVE-2026-108822 in Kamailio sipt module"
        author = "Valters IT"
        date = "2026-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-108822"
        cve = "CVE-2026-108822"
    strings:
        $isup_magic = { 01 00 } // ISUP message type indicator (example, adjust per protocol)
        $calling_party = "calling party" nocase
        $sipt = "sipt" nocase
    condition:
        $sipt and $calling_party and #isup_magic > 0
}

Suricata IDS Rule

alert udp any any -> any 5060 (msg:"CVE-2026-108822 Kamailio SIPT Buffer Overflow Attempt"; content:"|01 00|"; depth:2; content:"calling party"; nocase; offset:2; distance:0; content:"|0d 0a|"; within:100; sid:10000001; rev:1; metadata:created_at 2026_01_01, cve CVE-2026-108822;)

Elastic Detection

network where network.transport == "udp" and destination.port == 5060 and
  process.name == "kamailio" and
  network.payload contains "calling party" and
  length(network.payload) > 1500

Splunk SPL Query

index=network sourcetype=suricata event_type=alert signature="CVE-2026-108822*"
| stats count by src_ip, dest_ip, dest_port
| where count > 5

Wazuh OSSEC Rule

<group name="kamailio,">
  <rule id="100001" level="10">
    <decoded_as>json</decoded_as>
    <field name="event_type">sipt_parse_error</field>
    <field name="error_message">isup_get_calling_party</field>
    <description>CVE-2026-108822: Kamailio SIPT buffer overflow attempt detected</description>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 — UNPATCHED. No patch evidence from any tracked source; however, the NVD description indicates upgrading to 6.0.8 or 6.1.4 is sufficient.

1. Immediate mitigations:

   • Disable the sipt module if ISUP/SIP-I processing is not required (loadmodule "sipt.so" removal or comment out).
   • Restrict network access to the SIP listener (port 5060/5061) using firewall rules, allowing only trusted SIP peers.
   • Enable Kamailio's built-in memory debugging or compile with -fstack-protector-strong and -D_FORTIFY_SOURCE=2 to make exploitation harder.
   • Monitor logs for crashes or restarts of the Kamailio process.

2. Patch/upgrade steps:

   • Upgrade Kamailio to version 6.0.8 or 6.1.4 as advised by the vendor.
   • Apply the patch identified by commit 3667bebf8d0bea07ed16218fd921d07db87aeb21 if building from source.
   • After upgrade, verify the sipt module version and confirm the isup_get_calling_party function includes bounds checking.

3. Long-term hardening:

   • Implement strict input validation for all SIP and ISUP fields at the edge (e.g., using a SIP-aware firewall or SBC).
   • Regularly update Kamailio and monitor security advisories.
   • Segment VoIP infrastructure from general IT networks to limit lateral movement in case of compromise.
   • Conduct fuzz testing of the sipt module to uncover similar memory corruption issues.

References

1. NVD — CVE-2026-108822: https://nvd.nist.gov/vuln/detail/CVE-2026-108822
2. Kamailio Security Advisory (if available): https://www.kamailio.org/w/security/
3. Patch commit: https://github.com/kamailio/kamailio/commit/3667bebf8d0bea07ed16218fd921d07db87aeb21
4. CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer: https://cwe.mitre.org/data/definitions/119.html
5. CISA KEV: Not listed as of 2026-01-01. No known threat actor campaigns or exploit-in-the-wild evidence at this time.