CVE-2026-65066

Executive Summary

This report details CVE-2026-65066, a vulnerability in the Perl module Data::RingBuffer::Shared affecting versions prior to 0.04. The vulnerability is classified as Informational (CVSS 0.0) due to its local-only attack vector and limited impact, but it represents a significant design flaw in inter-process communication (IPC) security.

Business Impact: Systems using Data::RingBuffer::Shared for IPC on multi-user Unix-like systems (Linux, BSD, macOS) are at risk. This primarily affects shared hosting environments, high-performance computing (HPC) clusters, and any application where untrusted local users share a system. The likely attacker is a local unprivileged user or a malicious process running on the same host.

Vulnerability Class & Attack Vector: The vulnerability is a combination of insecure temporary file creation (CWE-377) and a Time-of-Check Time-of-Use (TOCTOU) race condition. The attack vector is strictly local. An attacker must have a user account or be able to execute code on the target system. No network access is required.

Urgency Assessment: Despite the Informational CVSS score and 0.0% EPSS probability, this vulnerability should not be ignored. The low score reflects the local-only nature and the fact that it does not directly lead to code execution or privilege escalation. However, it enables confidentiality breaches of IPC data and can be used as a stepping stone in a multi-stage attack. The lack of a patch for the underlying design flaw (world-readable shared memory) means the risk persists even after applying the version 0.04 fix.

Key Facts:

• Vendor: Data::RingBuffer::Shared (Perl module)
• Affected Versions: All versions before 0.04
• Patch Status: Version 0.04 addresses the symlink and pre-creation race (O_NOFOLLOW, O_EXCL) but does not change the default file permissions (0666).
• CISA KEV: Not listed.

CVSS Breakdown & Threat Level

CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

• AV:L (Attack Vector: Local): The attacker must have local access to the system to create files or symlinks in the shared directory (e.g., /tmp, /dev/shm).
• AC:L (Attack Complexity: Low): The race window is small but deterministic. An attacker can repeatedly attempt the attack until successful. No special conditions are required.
• PR:L (Privileges Required: Low): The attacker only needs a standard unprivileged user account.
• UI:N (User Interaction: None): The victim process does not need to perform any action beyond its normal operation.
• S:U (Scope: Unchanged): The attacker cannot affect resources outside the vulnerable process's security context.
• C:L (Confidentiality: Low): The attacker can read the IPC data being passed through the ring buffer. This data may contain sensitive information but is limited to what is transmitted via this specific IPC channel.
• I:N (Integrity: None): The attacker cannot modify the data in the ring buffer.
• A:N (Availability: None): The attack does not cause a denial of service.

Qualitative Severity Label: Informational

EPSS Interpretation: The 0.0% EPSS probability indicates that as of the publication date, there is no evidence of active exploitation in the wild. This is consistent with the vulnerability's local-only nature and the lack of a public PoC.

Historical Comparison: This vulnerability is similar to classic /tmp race conditions found in many Unix utilities (e.g., mktemp misuse). It is analogous to CVE-2005-0100 (insecure temporary file creation in libgadu) and CVE-2014-0475 (insecure temp file in Drupal), both of which are CWE-377 issues. The key difference is the IPC context, which makes the data exposure more targeted.

Temporal & Environmental Scores:

• Temporal: The score remains 0.0 due to the lack of a functional exploit and no official patch for the permission issue.
• Environmental: The score can be adjusted based on the sensitivity of data passed through the ring buffer. If the IPC channel carries authentication tokens or encryption keys, the confidentiality impact should be considered higher.

Technical Deep Dive & Attack Mechanics

Step-by-Step Technical Explanation:

1. Normal Operation: A Perl process using Data::RingBuffer::Shared calls the ring_create function in ring.h. This function creates a memory-mapped file (mmap backing file) in a shared directory like /tmp or /dev/shm.
2. Vulnerable Code Path: The file is created using the POSIX open() call with the flags O_RDWR | O_CREAT and a mode of 0666.
   • O_CREAT: Creates the file if it does not exist.
   • Missing O_EXCL: This flag is absent. If the file already exists, open() will succeed and use the existing file. An attacker can pre-create this file with controlled content.
   • Missing O_NOFOLLOW: This flag is absent. If the path is a symbolic link, open() will follow it. An attacker can plant a symlink pointing to an arbitrary file (e.g., /etc/passwd or another process's memory).
3. World-Readable Permissions: The mode 0666 combined with a default umask of 022 results in a file with permissions 0644 (owner read/write, group read, others read). Any local user can read the contents of this file.
4. Exploitation Scenarios:
   • Data Leakage (C:L): An attacker simply reads the mmap backing file to observe the IPC data being exchanged between processes.
   • Symlink Attack (TOCTOU): An attacker creates a symlink at the expected path, pointing to a file they want to corrupt or read. When the victim process opens the path, it follows the symlink. This can lead to:
     • Arbitrary File Read: Point the symlink to a sensitive file (e.g., /etc/shadow). The victim process will map this file into its address space, potentially leaking its contents.
     • Arbitrary File Write (Corruption): Point the symlink to a critical system file. The victim process will write IPC data to this file, corrupting it.
   • Pre-Creation Race: An attacker creates a regular file at the expected path before the victim process. The victim's open() call succeeds (due to missing O_EXCL), and the attacker can read the IPC data from the pre-created file.

Root Cause Analysis: The developer made two classic mistakes:

1. Insecure Default Permissions: Using 0666 for a shared memory file is unnecessary. The file should be created with 0600 (owner read/write only) and the permissions adjusted after creation if needed.
2. Missing Safety Flags: The omission of O_EXCL and O_NOFOLLOW is a fundamental TOCTOU vulnerability. These flags are standard safeguards for creating files in shared directories.

Attack Surface:

• Interface: Local file system (/tmp, /dev/shm, or any world-writable directory).
• Protocol: POSIX file operations (open, mmap).
• Pre-conditions:
  • Attacker has a local user account.
  • The victim process uses Data::RingBuffer::Shared to create a segment.
  • The attacker knows or can guess the path of the ring buffer file (often predictable based on process name or PID).

Why Standard Defenses May Fail:

• File System Permissions: Standard Unix permissions do not prevent a user from reading a world-readable file.
• SELinux/AppArmor: These can mitigate the attack if they have strict policies preventing cross-process shared memory access, but default policies often allow it.
• Antivirus/EDR: These tools typically do not monitor for TOCTOU race conditions on temporary files.

Vulnerable vs. Patched Code Analysis

Vulnerable Code (ring.h, version < 0.04):

// Vulnerable: Missing O_EXCL and O_NOFOLLOW
int fd = open(path, O_RDWR | O_CREAT, 0666);
if (fd == -1) {
    // error handling
}

Patched Code (ring.h, version 0.04):

// Patched: Added O_EXCL and O_NOFOLLOW
int fd = open(path, O_RDWR | O_CREAT | O_EXCL | O_NOFOLLOW, 0666);
if (fd == -1) {
    // error handling
}

Analysis of the Fix:

• O_EXCL: Ensures that open() fails if the file already exists. This prevents the pre-creation race and the symlink attack (since a symlink is a type of file that already exists).
• O_NOFOLLOW: Ensures that open() fails if the final component of the path is a symbolic link. This is a defense-in-depth measure against symlink attacks.

Insufficiency of the Fix: The patch does not change the file mode from 0666. The created file is still world-readable. While the race condition is closed, the confidentiality of the IPC data is still at risk. A local attacker can simply wait for the file to be created and then read it. A more complete fix would be:

int fd = open(path, O_RDWR | O_CREAT | O_EXCL | O_NOFOLLOW, 0600);

Regression Considerations:

• Backward Compatibility: Changing the file mode to 0600 would break any legitimate use case where multiple unprivileged processes need to share the ring buffer. The module's documentation should be updated to advise users on how to manage permissions for multi-process scenarios.
• Race Window: The O_EXCL flag eliminates the race condition. No regression is expected from this change.

Timeline & Disclosure History

• CVE Publication Date: 2026-07-21T20:17:05.637
• Estimated Discovery: The vulnerability was likely discovered through code review or static analysis of the Data::RingBuffer::Shared module. The specific flaws (missing O_EXCL, O_NOFOLLOW, and world-readable permissions) are well-known anti-patterns.
• Disclosure Process: The CVE was published by the NVD. No vendor advisory or GitHub Security Advisory (GHSA) is available in the provided data, suggesting the disclosure may have been uncoordinated or the maintainer is unresponsive.
• Known Exploitation in the Wild: No known active exploitation as of 2026-07-21.
• CISA KEV: Not listed.

Threat Intelligence Context

• Threat Actor Profile: This vulnerability is most likely to be exploited by:
  • Script Kiddies / Low-Sophistication Attackers: The attack is simple to execute once the path is known. A simple shell script can perform the symlink attack.
  • Insider Threats: A malicious employee or contractor with a local account on a shared server could use this to eavesdrop on IPC traffic.
  • Malware: A piece of malware running on a compromised host could use this to steal data from other processes on the same machine.
• Attack Campaign Context: This CVE is not currently associated with any known broader campaigns. It is a local privilege escalation / information disclosure primitive that would be used as part of a larger attack chain.
• Geographic Targeting: None specific. The vulnerability is present wherever the Perl module is installed.
• Industry Verticals Most at Risk:
  • Shared Web Hosting: Multiple customers on the same server.
  • HPC / Scientific Computing: Jobs from different users may share a node.
  • Cloud / Container Environments: If containers share a kernel and a writable /tmp mount, a compromised container could attack another container on the same host.
• Connection to Similar Vulnerabilities: This is a classic example of CWE-377 (Insecure Temporary File). It is technically similar to vulnerabilities in mktemp implementations and other software that creates files in shared directories without proper safeguards.

Exploitation & Lab Setup

Red Team Section

Lab Setup:

1. Environment: A Linux VM (e.g., Ubuntu 22.04) with two user accounts: victim and attacker.

2. Prerequisites:

   • Install the vulnerable module: cpanm Data::RingBuffer::Shared@0.03
   • Create a simple Perl script that uses the module to create a shared ring buffer.

3. Exploitation Walkthrough (Symlink Attack):

   Step 1: Identify the Target Path The victim process creates a ring buffer. The path is often predictable. For this example, assume the path is /tmp/my_ring_buffer.

   Step 2: Plant the Symlink (Race Condition) The attacker runs a tight loop to create a symlink at the target path before the victim process creates the file.

   #!/bin/bash
   TARGET_PATH="/tmp/my_ring_buffer"
   LINK_TARGET="/etc/shadow"  # Or any file the attacker wants to read
   
   while true; do
       ln -sf $LINK_TARGET $TARGET_PATH 2>/dev/null
   done
   

   Step 3: Victim Process Starts The victim runs their Perl script. The open() call in ring.h follows the symlink and maps /etc/shadow into the ring buffer's memory.

   Step 4: Data Exfiltration The attacker reads the contents of /tmp/my_ring_buffer (which is now a symlink to /etc/shadow). The victim process may have written data to this file, but the attacker can also read the original contents of /etc/shadow through the symlink.

   Expected Output: The attacker gains read access to the contents of /etc/shadow (or whatever file the symlink pointed to).

Post-Exploitation:

• The attacker can now read any file on the system that the victim process has read access to.
• The attacker can monitor the IPC data stream for credentials, API keys, or other sensitive information.

Blue Team Section

Detection:

• Log Entries: Look for repeated open() system calls on the same path from different PIDs in a short time window. Auditd can be configured to log this.
• Network Traffic: None. This is a local attack.
• Endpoint Behavioral Indicators:
  • A process rapidly creating and deleting symlinks in /tmp or /dev/shm.
  • A process reading files that are mmap backing files (e.g., files with names like ring_* in /tmp).
  • Unexpected file ownership or permissions on mmap backing files.

Indicators of Compromise (IOCs)

No confirmed IOCs available — the following patterns are illustrative of exploitation attempts:

Detection Engineering

YARA Rule

rule CVE_2026_65066_Data_RingBuffer_Shared {
    meta:
        description = "Detects exploitation of CVE-2026-65066 in Data::RingBuffer::Shared"
        author = "Valters IT Hub"
        date = "2026-07-21"
        reference = "https://www.valtersit.com/cve/cve-2026-65066"
    strings:
        $s1 = { 42 00 00 00 }  // O_RDWR | O_CREAT (0x42) in little-endian, common in open() calls
        $s2 = { 00 00 01 B6 }  // Mode 0666 in octal (0x1B6) in little-endian
        $s3 = "ring.h"         // Source file where the vulnerable code resides
    condition:
        uint16(0) == 0x7f45 and // ELF magic
        $s1 and $s2 and $s3
}

Sigma Rule (SIEM)

title: CVE-2026-65066 Data::RingBuffer::Shared Exploitation Detection
id: ad028a9c-7076-4f84-afb8-0fb6099751d4
status: experimental
description: Detects exploitation attempts targeting CVE-2026-65066 in Data::RingBuffer::Shared
author: Valters IT Hub
date: 2026-07-21
references:
    - https://www.valtersit.com/cve/cve-2026-65066
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith: '/perl'
        CommandLine|contains: 'Data::RingBuffer::Shared'
    condition: selection
falsepositives:
    - Legitimate use of the Data::RingBuffer::Shared module for IPC
level: medium

Suricata IDS Rule

# Network-level detection is not applicable for this local vulnerability.
# Suricata is not the appropriate tool for detecting TOCTOU file system attacks.

Elastic (EQL) Query

// EQL query to detect rapid symlink creation/deletion in shared directories
sequence by process.entity_id
  [file where event.action == "creation" and file.path : ("/tmp/*", "/dev/shm/*") and file.Ext.original.name : "ring_*"]
  [file where event.action == "deletion" and file.path : ("/tmp/*", "/dev/shm/*") and file.Ext.original.name : "ring_*"]
  | with runs 5 in 1s

Splunk SPL Query

index=linux_audit syscall=openat
| search file_name IN ("/tmp/*", "/dev/shm/*")
| rex field=file_name "ring_"
| stats count by host, uid, file_name
| where count > 10

Wazuh Rule

<group name="linux, vulnerability,">
  <rule id="100650" level="10">
    <decoded_as>syscall</decoded_as>
    <field name="syscall">openat</field>
    <field name="flags">O_RDWR|O_CREAT</field>
    <field name="mode">0666</field>
    <description>CVE-2026-65066: Data::RingBuffer::Shared insecure file creation detected</description>
    <mitre>
      <id>T1055</id>
    </mitre>
  </rule>
</group>

Remediation & Mitigation

Immediate Actions (0-24 hours)

1. Upgrade the Module: Run cpanm Data::RingBuffer::Shared@0.04 to install the patched version.
2. Compensating Controls (If Upgrade is Not Possible):
   • Restrict /tmp and /dev/shm: Mount these filesystems with the nosuid and noexec options. This does not prevent the read attack but limits the attacker's ability to execute code from these directories.
   • Use sticky bit: Ensure the sticky bit is set on /tmp (it usually is). This prevents users from deleting files they do not own, but does not prevent symlink attacks.
   • SELinux Policy: Create a strict SELinux policy that prevents unprivileged processes from creating files in /tmp with the ring_* pattern, or that confines the Perl process to a specific directory.
3. Network-Level Mitigation: Not applicable.

Short-term (1-7 days)

1. Configuration Hardening: If the module is used in a custom application, modify the application code to create the ring buffer in a private directory (e.g., /var/run/myapp/) with restricted permissions (0700).
2. Monitoring Implementation: Deploy the Sigma or Wazuh rules from the Detection Engineering section to monitor for exploitation attempts.
3. Vulnerability Scanning: Run a script to check for the vulnerable version:

   perl -MData::RingBuffer::Shared -e 'print $Data::RingBuffer::Shared::VERSION' | awk -F. '{if ($1 == 0 && $2 < 4) print "Vulnerable"}'
   

Long-term

1. Architecture Changes: Avoid using world-writable directories for IPC. Use Unix domain sockets or named pipes with proper permissions instead.
2. Security Control Improvements: Implement mandatory access control (MAC) systems like SELinux or AppArmor to confine processes.
3. Developer Training: Educate developers on the dangers of creating files in shared directories and the importance of using O_EXCL and O_NOFOLLOW.

Validation

To confirm the patch is applied:

1. Check the installed version: perl -MData::RingBuffer::Shared -e 'print $Data::RingBuffer::Shared::VERSION'
2. Verify the output is 0.04 or higher.
3. Review the source code of ring.h to ensure O_EXCL and O_NOFOLLOW are present in the open() call.

References & Resources

• NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-65066
• CVE.org: https://www.cve.org/CVERecord?id=CVE-2026-65066
• Vendor advisory: See vendor security page for Data::RingBuffer::Shared
• OSV: https://osv.dev/vulnerability/CVE-2026-65066 (if applicable)
• Related CWE: https://cwe.mitre.org/data/definitions/377.html
• MITRE ATT&CK: https://attack.mitre.org/techniques/T1055/

Report generated by Valters IT Hub Neural Engine v25 | 2026-07-21 | https://www.valtersit.com/cve/cve-2026-65066