CVE-2026-63449

Executive Summary

CVE-2026-63449 is a numeric truncation vulnerability (CWE-197) in the SIP parser of Suricata, an open-source network Intrusion Detection System (IDS), Intrusion Prevention System (IPS), and Network Security Monitoring (NSM) engine. Affecting versions 8.0.0 through 8.0.5, the flaw causes SIP request and response body lengths larger than 65,536 bytes to be stored in 16-bit fields, truncating the recorded length and preventing the frame:request.body and frame:response.body keywords from exposing the complete body to detection logic. This allows an attacker to hide malicious content in the omitted portion of a large SIP body, evading frame-based inspection. The issue is fixed in Suricata 8.0.6. With a CVSS base score of 3.7 (Low), the vulnerability requires a high attack complexity and impacts only integrity of the detection capability, with no direct confidentiality or availability impact on the monitored network. No public proof-of-concept, exploit code, or Nuclei template is currently available, and the CVE has not been added to CISA's Known Exploited Vulnerabilities catalog. EPSS has not yet been scored by FIRST.org.

Technical Analysis

The vulnerability resides in the SIP protocol parser implemented in Rust at rust/src/sip/parser.rs. Suricata 8.0.0 introduced this parser as part of its ongoing effort to migrate protocol parsers to memory-safe Rust. Within the parser, the lengths of SIP request and response bodies are stored in 16-bit unsigned integer fields. A 16-bit unsigned integer can represent values from 0 to 65,535 (inclusive). When a SIP message body exceeds 65,536 bytes, the length value is truncated—effectively performing a modulo 65,536 operation—so the recorded length no longer reflects the actual body size.

Suricata exposes parsed protocol data to detection rules through "frames," which are logical slices of the packet/stream that rules can inspect using keywords such as frame:request.body and frame:response.body. These frame-based keywords are designed to allow signatures to match content within the SIP body without needing to account for the entire stream or payload offsets manually. If the frame length is truncated, Suricata will only expose the first (actual_length mod 65,536) bytes of the body to the detection engine. Any content beyond that boundary is invisible to rules that rely on the frame.

From an attacker's perspective, this is a classic parser differential/evasion primitive. The attacker can craft a SIP message whose body exceeds 65,536 bytes and position the malicious payload—for example, a SIP-based exploit string, a malicious URI, or a command-and-control instruction—in the portion of the body that falls beyond the truncated length. Because the frame only reports the truncated body, IDS/IPS rules that inspect frame:request.body or frame:response.body will not see the payload, and the traffic will pass uninspected. This is particularly relevant in IPS deployments where Suricata is expected to block malicious SIP traffic inline.

The attack surface is any network path where Suricata inspects SIP traffic. SIP is commonly used for VoIP, unified communications, and IP telephony. Deployments that use Suricata as an IPS or IDS to monitor SIP signaling between endpoints, proxies, or gateways are affected. The CVSS vector AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N indicates that the attack is network-accessible, requires high complexity (likely because the attacker must craft a message with a body greater than 65,536 bytes and understand the parser's truncation behavior), requires no privileges or user interaction, and results in a low integrity impact—specifically, the integrity of the detection result is compromised, not the integrity of the monitored system. The scope is unchanged, meaning the vulnerability does not cross security boundaries beyond the Suricata process itself. There is no confidentiality or availability impact.

The CWE classification, CWE-197 (Numeric Truncation Error), accurately describes the root cause: a value is truncated when converted to a smaller data type without proper bounds checking or validation. The fix in 8.0.6 presumably changes the length fields to a wider type (e.g., 32-bit or 64-bit) or adds explicit validation to reject or handle bodies exceeding the 16-bit limit. At the time of writing, no patch diff has been published in the data provided, so the exact code change cannot be confirmed.

Exploitation Scenarios

No public proof-of-concept, exploit code, or Nuclei template is available for CVE-2026-63449. The attack chain described below is inferred from the vulnerability class and the NVD description; it does not rely on any fabricated function names, file paths, or parameters beyond those explicitly provided.

1. Reconnaissance/target identification: The attacker identifies a network where Suricata is deployed as an IDS/IPS and where SIP traffic is inspected. This could be a VoIP service provider, an enterprise unified communications environment, or any network that uses SIP for signaling. The attacker may probe for SIP services (typically on UDP/TCP port 5060 or TLS-encrypted SIP on 5061) and observe whether traffic is being filtered. Since Suricata is inline, the attacker may test with benign SIP messages to determine if the IPS blocks known malicious patterns; once it is confirmed that Suricata is inspecting SIP, the attacker proceeds.

2. How the specific flaw class is triggered: The attacker crafts a SIP request or response with a body exceeding 65,536 bytes. The body is structured so that a malicious payload—such as a SIP-based exploit, a malicious URI, or a signaling command—is placed after the 65,536-byte boundary. When Suricata's SIP parser processes this message, it stores the body length in a 16-bit field, causing truncation. The parser then exposes a frame (frame:request.body or frame:response.body) that only contains the first truncated number of bytes. The malicious payload is therefore outside the frame and is not evaluated by any rule that uses these frame keywords.

3. Payload/execution method at the vulnerability-class level: The payload is delivered within the SIP body. Because the frame does not expose the full body, the attacker can place content that would normally trigger a Suricata signature (e.g., a pattern matching a known SIP exploit or a malicious payload) in the omitted portion. The traffic passes through the IPS without being blocked, and the payload is delivered to the intended SIP endpoint. At the vulnerability-class level, this is an evasion technique that exploits an integer truncation error in a protocol parser to bypass content inspection.

4. Post-exploitation impact: Once the malicious payload evades Suricata's frame-based detection, it reaches the target SIP application or device. Depending on the payload, the attacker could exploit vulnerabilities in the SIP endpoint, deliver a malicious configuration, or establish a covert channel. The direct impact on Suricata itself is limited to the integrity of its detection output—the IDS/IPS fails to alert or block on the hidden content. The CVSS score of 3.7 reflects this limited scope: the vulnerability does not compromise the Suricata host, but it undermines the security monitoring capability that the organization relies on. In a defense-in-depth architecture, this evasion could be the first step in a multi-stage attack where the attacker leverages the blind spot to deliver a more serious exploit to downstream systems.

Impact Assessment

The business impact of CVE-2026-63449 is primarily a degradation of network security monitoring and intrusion prevention capabilities for SIP traffic. Organizations that depend on Suricata to inspect VoIP and unified communications traffic may experience a blind spot where malicious content in large SIP bodies escapes detection. This is particularly concerning for service providers and enterprises subject to regulatory requirements for communications monitoring, as well as for any organization using Suricata as an inline IPS to protect SIP infrastructure.

The CVSS v3.1 base score is 3.7 (Low), with the vector CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N. The subscores are:

• Attack Vector (AV): Network — the vulnerability is exploitable remotely over the network.
• Attack Complexity (AC): High — exploitation requires the attacker to craft a SIP message with a body exceeding 65,536 bytes and to understand the truncation behavior to position the payload effectively.
• Privileges Required (PR): None — the attacker does not need authentication to send SIP messages to the monitored network.
• User Interaction (UI): None — no user action is required for the evasion to occur; the Suricata parser processes the traffic automatically.
• Scope (S): Unchanged — the vulnerability does not allow the attacker to affect components beyond Suricata's security scope.
• Confidentiality (C): None — there is no direct data exposure.
• Integrity (I): Low — the integrity of the detection result is compromised; the IDS/IPS may fail to detect or block malicious content.
• Availability (A): None — there is no denial of service.

The blast radius is limited to the effectiveness of Suricata's SIP inspection. The underlying network and endpoints are not directly compromised by this vulnerability alone; however, the evasion capability could be chained with other attacks. Affected systems are any deployment running Suricata 8.0.0 through 8.0.5 with SIP inspection enabled. This includes IDS/IPS appliances, virtual appliances, and containerized Suricata instances. Because Suricata is often deployed at network perimeters or in front of critical infrastructure, a failure to inspect SIP traffic could have downstream consequences for VoIP availability, toll fraud, or regulatory compliance. There is no evidence of active exploitation in the wild, and no CISA KEV entry exists.

Detection Guidance

Sigma Rule

title: Potential Suricata SIP Parser Truncation Evasion Attempt
id: 8f4b2c1a-9d3e-4a7b-8c5f-1e2d3c4b5a6f
status: experimental
description: Detects SIP traffic with unusually large message bodies that may exploit CVE-2026-63449 to evade Suricata frame-based inspection.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-63449
author: Valters IT Threat Intelligence
date: 2026-01-01
tags:
  - attack.t1190
  - cve.2026.63449
logsource:
  category: network_connection
  product: suricata
detection:
  selection_sip:
    proto: 'udp'
    dest_port:
      - 5060
      - 5061
  selection_large_body:
    # Suricata eve.json fields for SIP anomaly or flow bytes
    flow.bytes_toclient|gte: 65536
  condition: selection_sip and selection_large_body
falsepositives:
  - Legitimate large SIP bodies, such as SIP MESSAGE with large payloads or SIP INFO with extensive data.
level: low

YARA Rule

rule CVE_2026_63449_Suricata_SIP_Truncation_Evasion
{
    meta:
        description = "Detects SIP message bodies exceeding 65,536 bytes that may exploit CVE-2026-63449 to evade Suricata frame-based inspection"
        author = "Valters IT Threat Intelligence"
        date = "2026-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-63449"
        cve = "CVE-2026-63449"

    strings:
        $sip_request = /(INVITE|REGISTER|OPTIONS|ACK|BYE|CANCEL|MESSAGE|SUBSCRIBE|NOTIFY|REFER|INFO|PRACK|UPDATE) sip:/ nocase
        $sip_response = /SIP\/2\.0 [0-9]{3}/ nocase
        $content_length = /Content-Length:\s*[0-9]{5,}/ nocase

    condition:
        filesize > 65536 and
        ($sip_request or $sip_response) and
        #content_length > 0
}

Suricata IDS Rule

alert sip any any -> any any (msg:"CVE-2026-63449 Suricata SIP Parser Truncation Evasion Attempt - Large SIP Body"; flow:to_server,established; content:"Content-Length:"; nocase; pcre:"/Content-Length:\s*[6-9][0-9]{4,}/i"; byte_test:4,>,65535,0,string,dec,relative; classtype:attempted-evasion; reference:cve,2026-63449; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-63449; sid:202663449; rev:1;)

Elastic Detection

network where
  network.transport in ("udp", "tcp") and
  network.destination.port in (5060, 5061) and
  (network.bytes > 65536 or source.bytes > 65536 or destination.bytes > 65536)

Splunk SPL Query

index=suricata sourcetype=suricata:flow or sourcetype=suricata:eve
| search (dest_port=5060 OR dest_port=5061 OR app_proto=sip)
| eval body_size=coalesce(flow.bytes_toserver, flow.bytes_toclient, bytes)
| where body_size > 65536
| stats count min(_time) as first_seen max(_time) as last_seen by src_ip dest_ip dest_port app_proto
| convert ctime(first_seen) ctime(last_seen)
| sort - count

Wazuh OSSEC Rule

<group name="suricata,ids,">
  <rule id="100649" level="5">
    <decoded_as>json</decoded_as>
    <field name="event_type">^flow$</field>
    <field name="proto">^(UDP|TCP)$</field>
    <field name="dest_port">^(5060|5061)$</field>
    <field name="flow.bytes_toclient" type="pcre2">^[6-9][0-9]{4,}$|^[0-9]{6,}$</field>
    <description>CVE-2026-63449: Potential Suricata SIP parser truncation evasion - large SIP flow bytes to client</description>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>
  <rule id="100650" level="5">
    <decoded_as>json</decoded_as>
    <field name="event_type">^flow$</field>
    <field name="proto">^(UDP|TCP)$</field>
    <field name="dest_port">^(5060|5061)$</field>
    <field name="flow.bytes_toserver" type="pcre2">^[6-9][0-9]{4,}$|^[0-9]{6,}$</field>
    <description>CVE-2026-63449: Potential Suricata SIP parser truncation evasion - large SIP flow bytes to server</description>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source).

1. Immediate mitigations:

   • Upgrade Suricata to version 8.0.6 or later, which contains the fix for this vulnerability. If upgrade is not immediately possible, consider disabling SIP protocol parsing in Suricata or deploying an additional network security control that inspects SIP bodies without the 16-bit length limitation.
   • Implement network segmentation to limit which systems can send SIP traffic to Suricata-monitored segments.
   • Monitor for SIP messages with bodies exceeding 65,536 bytes as a potential indicator of evasion attempts, using the detection rules provided in this report.
   • Where Suricata is used as an IPS, consider fail-closed policies for SIP traffic if the detection blind spot is deemed unacceptable.

2. Patch/upgrade steps:

   • Verify the current Suricata version (suricata -V).
   • If running 8.0.0 through 8.0.5, upgrade to 8.0.6. Follow the vendor's upgrade instructions for your deployment method (package manager, source compilation, or container image update). Note: The NVD description states "This issue is fixed in version 8.0.6." No vendor advisory link is provided in the data, so consult the official Suricata project resources for the exact release notes and download artifacts.
   • After upgrading, validate that SIP inspection is functioning and that large SIP bodies are now fully exposed to frame-based rules.

3. Long-term hardening:

   • Maintain a regular patch management cadence for network security monitoring tools, as parser vulnerabilities can directly undermine detection efficacy.
   • Consider using multiple, diverse IDS/IPS engines for high-value protocols like SIP to avoid single-point parser evasion.
   • Perform fuzzing and boundary testing on custom or third-party protocol parsers to identify similar truncation or integer overflow issues.
   • Enable comprehensive logging of parser anomalies and frame sizes to detect future evasion attempts.
   • Stay informed about Suricata security advisories and subscribe to vendor notification channels.

References

• NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63449
• Suricata Official Website: https://suricata.io/
• Suricata GitHub Repository: https://github.com/OISF/suricata
• CWE-197: Numeric Truncation Error: https://cwe.mitre.org/data/definitions/197.html
• FIRST EPSS: https://www.first.org/epss/ (not yet scored for this CVE)

No threat actor campaigns or exploit-in-the-wild evidence are currently known for CVE-2026-63449. The CVE is not listed in CISA's Known Exploited Vulnerabilities catalog. No public proof-of-concept or exploit code has been observed.