CVE-2026-33792

Executive Summary

CVE-2026-33792 is a stack-based buffer overflow (CWE-121) in the srxpfe process of Juniper Networks Junos OS running on SRX Series services gateways. An unauthenticated network attacker can trigger the flaw by sending a crafted packet to a configured GRE tunnel, achieving remote code execution as root or inducing a denial of service. With a CVSS v3.1 base score of 9.8 (Critical) and no patch, no workaround, and no public exploit currently available, any SRX device with a GRE tunnel exposed to untrusted networks represents a high-priority exposure.

Technical Analysis

The vulnerability resides in srxpfe, the SRX Series packet forwarding engine daemon responsible for data-plane processing on Junos OS SRX platforms. The defect is classified as CWE-121 (Stack-based Buffer Overflow), meaning that input data — delivered here as a crafted network packet received over a configured GRE tunnel — is copied into a fixed-length stack buffer without adequate bounds validation. When the input exceeds the buffer's capacity, adjacent stack memory is overwritten.

Several attributes of this vulnerability amplify its severity:

• Pre-authentication, network-reachable trigger. The CVSS vector AV:N/AC:L/PR:N/UI:N confirms the attack is launched over the network with no authentication and no user interaction. The GRE tunnel itself provides the delivery vector.
• Root-level execution context. Per the vendor description, successful exploitation allows code execution "as root." The srxpfe process operates within the packet-processing path, and compromise of this component yields privileged control over the device.
• Data-plane attack surface. Because the trigger is a packet processed through a configured GRE tunnel, the flaw is reachable wherever GRE is enabled and reachable from an untrusted network segment — a common configuration for WAN overlay and site-to-site interconnect scenarios.
• Dual impact. The same memory-corruption primitive can produce either a denial of service (crash/restart of the forwarding process) or full remote code execution, depending on the crafted payload.

The specific stack buffer size, the exact packet field or encapsulation layer parsed by srxpfe that overflows, and any offset or control-flow details are not disclosed in the available NVD description or CNA title. These implementation specifics are intentionally withheld pending a vendor fix. No public proof-of-concept, exploit code, or Nuclei template is currently available, and the vulnerability has not been scored by FIRST.org (EPSS not yet assigned) nor added to CISA KEV.

Exploitation Scenarios

No public PoC is available; the attack chain below is inferred from the vulnerability class (CWE-121) and the vendor description, and does not rely on fabricated implementation details.

1. Reconnaissance / target identification. An attacker identifies Juniper SRX Series devices that have a GRE tunnel configured and reachable from an untrusted network. Fingerprinting of SRX management and data-plane interfaces, combined with GRE endpoint discovery (IP protocol 47), narrows candidate targets. Public scanning services can enumerate devices advertising Juniper SRX characteristics.

2. Triggering the flaw. The attacker transmits a crafted packet into the target's configured GRE tunnel. Because the tunnel is the delivery path, the attacker needs only the ability to send GRE-encapsulated traffic to the tunnel endpoint — no credentials, session, or user interaction are required. The malformed packet reaches srxpfe and is processed by the vulnerable parsing routine, causing input to be copied past the bounds of a fixed-length stack buffer.

3. Payload / execution (class-level). As with any stack-based buffer overflow, the overflow overwrites adjacent stack memory. At the vulnerability-class level, this enables the attacker to corrupt control data (such as a return address or saved state) and redirect execution. Where protections permit, the attacker can achieve arbitrary code execution in the context of the srxpfe process — which runs with root privileges — or, minimally, force the process to crash. The precise technique for controlling execution flow is not publicly documented for this CVE.

4. Post-exploitation impact. Successful code execution as root grants the attacker full control of the SRX device: the ability to manipulate forwarding policy, inspect or redirect traffic traversing the gateway, persist on the appliance, and pivot into protected network segments. A denial-of-service outcome is equally available and requires no privilege escalation — a simple crash of srxpfe degrades or halts packet forwarding.

Impact Assessment

With a CVSS v3.1 base score of 9.8 (Critical), the impact subscores are Confidentiality: High, Integrity: High, and Availability: High, with Scope: Unchanged. This reflects a worst-case combination: an unauthenticated, remote, low-complexity attack that can yield root-level compromise of a perimeter security device.

• Business impact. Compromise of an SRX gateway undermines the trust boundary it is meant to enforce. An attacker with root on the device can intercept, alter, or block traffic, disable security controls, and use the appliance as a foothold for lateral movement.
• Affected systems. Juniper Networks SRX Series platforms running Junos OS where a GRE tunnel is configured and reachable. Devices without an exposed GRE tunnel are not reachable via the described vector.
• Blast radius. Because SRX devices typically sit at network perimeters and aggregation points, a single compromised unit can expose entire downstream segments. GRE tunnels are commonly used for WAN overlays, branch interconnect, and cloud connectivity, broadening the potential attack surface across distributed deployments.
• Exploitability outlook. No public exploit, PoC, or Nuclei template currently exists, and EPSS is unscored. However, the pre-auth, network-reachable, root-execution profile makes this an attractive target for both opportunistic scanning and targeted actors once technical details emerge.

Detection Guidance

Sigma Rule

title: Juniper SRX srxpfe GRE Tunnel Stack Buffer Overflow Attempt
id: cve-2026-33792-srxpfe-gre
status: experimental
description: Detects anomalous or malformed GRE-encapsulated traffic targeting Juniper SRX devices that may trigger CVE-2026-33792 in the srxpfe process.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-33792
author: valtersit.com
date: 2026/01/01
logsource:
  category: network_connection
  product: suricata
detection:
  selection_proto:
    proto: gre
  selection_alert:
    alert.signature_id:
      - 9000001
  condition: selection_proto and selection_alert
fields:
  - src_ip
  - dest_ip
  - proto
falsepositives:
  - Legitimate GRE traffic that triggers an IDS signature heuristic
level: high

YARA Rule

rule CVE_2026_33792_SRX_SRXPFE_GRE_Overflow
{
    meta:
        description = "Generic detection aid for CVE-2026-33792 Juniper SRX srxpfe stack buffer overflow via crafted GRE tunnel packet"
        author = "valtersit.com"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-33792"
        date = "2026-01-01"
        cve = "CVE-2026-33792"
    strings:
        $gre = { 08 00 45 00 }        // outer IPv4 header (common GRE transport)
        $sig1 = "srxpfe" nocase
        $sig2 = "Junos" nocase
    condition:
        uint16(0) == 0x0800 and
        ( $sig1 or $sig2 ) and
        #gre > 0
}

Suricata IDS Rule

alert gre any any -> any any (msg:"CVE-2026-33792 Juniper SRX srxpfe GRE Stack Buffer Overflow Attempt"; flow:to_server; dsize:>1400; threshold: type limit, track by_src, count 1, seconds 60; reference:cve,2026-33792; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-33792; classtype:attempted-admin; sid:9000001; rev:1;)

Elastic Detection

network where network.transport == "gre" and event.action == "network_flow" and
  source.ip != null and destination.port != 0 and
  network.bytes > 1400

This EQL query surfaces oversized GRE flows toward monitored SRX endpoints; correlate with IDS alerts (signature sid 9000001) for confirmation.

Splunk SPL Query

index=network sourcetype=suricata OR sourcetype=pan:traffic
| search (proto=gre OR protocol=47) 
| stats count min(_time) as first_seen max(_time) as last_seen by src_ip dest_ip 
| where count > 0
| eval cve="CVE-2026-33792", severity="HIGH"
| table src_ip dest_ip count first_seen last_seen cve severity
| sort - count

Wazuh OSSEC Rule

<group name="juniper,srx,cve-2026-33792,">
  <rule id="100701" level="12">
    <decoded_as>json</decoded_as>
    <field name="alert.signature">srxpfe</field>
    <description>CVE-2026-33792: Potential Juniper SRX srxpfe GRE stack buffer overflow activity detected</description>
    <mitre>
      <id>T1190</id>
    </mitre>
    <group>exploit_attempt,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 — UNPATCHED. No patch evidence from any tracked source. Vendor fix, workarounds, and affected version ranges are not available in the provided data.

1. Immediate mitigations

   • Restrict or disable GRE tunnels on SRX Series devices wherever they are not strictly required. Where GRE is required, apply infrastructure ACLs so that only trusted, known peer addresses can send GRE (IP protocol 47) traffic to the tunnel endpoint.
   • Block inbound GRE from untrusted internet-facing interfaces at upstream routers/firewalls.
   • Segment management and data-plane access; monitor srxpfe for unexpected restarts or crashes as an early DoS indicator.
   • Increase logging and alerting on GRE traffic anomalies while awaiting a vendor fix.

2. Patch / upgrade steps

   • No patch is currently available. Monitor Juniper's official security advisories and the JSA/Security Advisories portal for a fixed Junos OS release addressing CVE-2026-33792.
   • When Juniper publishes a fix, validate the affected-version matrix, schedule maintenance-window upgrades, and confirm the srxpfe process version post-upgrade.

3. Long-term hardening

   • Enforce a least-exposure network architecture: terminate GRE tunnels on hardened, access-controlled endpoints only.
   • Apply defense-in-depth (segmentation, egress filtering, strict ACLs) so that compromise of a single appliance does not grant broad lateral movement.
   • Integrate Junos security advisories into vulnerability management workflows and maintain an accurate SRX asset inventory to accelerate future patch cycles.

References

• NVD — CVE-2026-33792: https://nvd.nist.gov/vuln/detail/CVE-2026-33792
• MITRE CWE-121 (Stack-based Buffer Overflow): https://cwe.mitre.org/data/definitions/121.html
• MITRE ATT&CK T1190 — Exploit Public-Facing Application: https://attack.mitre.org/techniques/T1190/
• Juniper Networks Security Advisories (monitor for the CVE-2026-33792 JSA): https://supportportal.juniper.net/s/security-advisories
• CISA Known Exploited Vulnerabilities Catalog (check status): https://www.cisa.gov/known-exploited-vulnerabilities-catalog

As of this report, there is no evidence of exploitation in the wild, no public proof-of-concept, and CVE-2026-33792 is not listed in CISA KEV. No associated threat actor campaigns have been identified in the available data.