SUSE Curl Authentication Bypass and OpenSSL Flaws (SUSE-2026-23521-1): Patching and Detection Guide

---
title: Suspicious Curl Usage with Insecure or Credential Flags on Linux
id: 3f7b2e91-4c5a-4d8e-b6f1-9a2c8d3e5f07
status: experimental
description: Detects curl invocations that disable TLS verification or embed credentials directly on the command line — patterns associated with defense evasion, payload staging, and abuse of automation following client-side TLS/auth weaknesses.
references:
  - https://linuxsecurity.com/advisories/suse/suse-2026-23521-1-low-for-curl
  - https://attack.mitre.org/techniques/T1105/
  - https://attack.mitre.org/techniques/T1552/001/
author: Security Arsenal
date: 2026/04/06
tags:
  - attack.command_and_control
  - attack.t1105
  - attack.credential_access
  - attack.t1552.001
logsource:
  category: process_creation
  product: linux
  service: auditd
detection:
  selection_img:
    - Image|endswith: '/curl'
  selection_insecure:
    CommandLine|contains:
      - ' --insecure'
      - ' -k '
      - '--insecure '
  selection_creds:
    CommandLine|contains:
      - ' -u '
      - '--user '
      - '://'
      - '@'
  condition: selection_img and (selection_insecure or selection_creds)
falsepositives:
  - Legitimate automation scripts with embedded basic-auth credentials (inventory and migrate these to credential stores)
  - Dev/test systems hitting internal endpoints with self-signed certificates
level: medium
---
title: Curl Execution from Unusual Parent Process on Linux
id: 8c1d4a62-7e3b-4f09-a2d5-6b9e1c4f8a03
status: experimental
description: Detects curl spawned by web servers, script interpreters, or other parents that do not normally perform outbound transfers — a common post-exploitation payload retrieval pattern relevant when client-side flaws in transfer tooling are in scope.
references:
  - https://linuxsecurity.com/advisories/suse/suse-2026-23521-1-low-for-curl
  - https://attack.mitre.org/techniques/T1105/
author: Security Arsenal
date: 2026/04/06
tags:
  - attack.command_and_control
  - attack.t1105
logsource:
  category: process_creation
  product: linux
  service: auditd
detection:
  selection_img:
    Image|endswith: '/curl'
  selection_parent:
    ParentImage|endswith:
      - '/httpd'
      - '/apache2'
      - '/nginx'
      - '/php-fpm'
      - '/tomcat'
      - '/node'
      - '/python'
      - '/perl'
  condition: selection_img and selection_parent
falsepositives:
  - Health-check or monitoring plugins executed by the web stack
  - Application runtimes legitimately shelling out to curl (recommend migrating to library calls and alerting until migrated)
level: medium

// Hunt: unpatched curl risk posture + suspicious curl execution across SUSE fleet
// Requires Syslog/auditd ingestion into Sentinel (CEF or Azure Monitor Agent)

// Part 1: Suspicious curl command lines (TLS bypass flags / embedded creds)
Syslog
| where TimeGenerated > ago(7d)
| where ProcessName =~ "curl"
| extend CmdLine = tostring(SyslogMessage)
| where CmdLine has_any ("--insecure", " -k ", " --user ", " -u ")
| project TimeGenerated, Computer, ProcessName, CmdLine
| sort by TimeGenerated desc;

// Part 2: curl spawned by web/script parents (payload staging behavior)
DeviceProcessEvents
| where TimeGenerated > ago(7d)
| where FileName =~ "curl"
| where InitiatingProcessFileName in~ ("httpd", "apache2", "nginx", "php-fpm", "node", "python", "perl", "tomcat")
| project TimeGenerated, DeviceName, InitiatingProcessFileName, ProcessCommandLine, AccountName
| sort by TimeGenerated desc;

// Part 3: Identify hosts that have NOT yet logged a successful curl package update via zypper
// (Tune the package string to your SUSE patch stream)
Syslog
| where TimeGenerated > ago(14d)
| where SyslogMessage has "zypper" and SyslogMessage has "curl"
| summarize LastZypperCurlActivity = max(TimeGenerated) by Computer
| where LastZypperCurlActivity < ago(7d)
| sort by LastZypperCurlActivity asc

-- Hunt: enumerate curl version and package state across Linux endpoints
-- Deploy as a Velociraptor hunt; flags hosts still running pre-patch curl builds

SELECT Hostname,
       Fqdn,
       split(string=Stdout, sep=" ")[1] AS CurlVersion,
       Stdout AS RawVersionString
FROM execve(argv=["/bin/sh", "-c", "curl --version | head -1"])

-- Companion artifact: check RPM database for curl package version and install time
SELECT Hostname,
       Stdout AS CurlRpmInfo
FROM execve(argv=["/bin/sh", "-c", "rpm -q --queryformat '%{NAME} %{VERSION}-%{RELEASE} %{INSTALLTIME:date}\n' curl libcurl4 2>/dev/null"])

-- Companion artifact: find processes currently linked against libcurl
-- (identifies runtime consumers that need service restart after patching)
SELECT Pid, Name, Exe, Username
FROM pslist()
WHERE Name =~ 'curl'
   OR Exe =~ 'curl'

#!/bin/bash
# SUSE-2026-23521-1 remediation and verification script
# Run on SLES / openSUSE systems. Requires root or sudo.

set -euo pipefail

echo "=== [1/5] Current curl/libcurl package state ==="
rpm -q curl libcurl4 2>/dev/null || echo "curl packages not found via rpm"

echo "=== [2/5] Refreshing repositories and checking for available curl patches ==="
zypper refresh
zypper list-patches --cve 2>/dev/null | grep -i curl || echo "No curl-specific patch flag found via CVE listing; proceeding with package update"

echo "=== [3/5] Applying curl update ==="
zypper --non-interactive update curl libcurl4

echo "=== [4/5] Post-patch verification ==="
INSTALLED_VER=$(curl --version | head -1)
echo "Binary reports: ${INSTALLED_VER}"
rpm -q --queryformat '%{NAME}-%{VERSION}-%{RELEASE} installed %{INSTALLTIME:date}\n' curl libcurl4

# Verify the package changelog references the current maintenance update
rpm -q --changelog curl | head -20

echo "=== [5/5] Identifying running processes linked to libcurl (restart candidates) ==="
# libcurl consumers keep the OLD library mapped until restarted
for pid in $(ls /proc | grep -E '^[0-9]+$'); do
  if grep -qs 'libcurl' /proc/"$pid"/maps 2>/dev/null; then
    comm=$(cat /proc/"$pid"/comm 2>/dev/null)
    deleted=$(grep -c 'libcurl.*(deleted)' /proc/"$pid"/maps 2>/dev/null || true)
    if [ "$deleted" -gt 0 ]; then
      echo "STALE: PID $pid ($comm) still mapped to pre-patch libcurl — restart this service"
    fi
  fi
done

echo ""
echo "=== Remediation notes ==="
echo "- Reboot or restart flagged services so libcurl consumers load the patched library."
echo "- Rebuild/repull SUSE-based container images; patched hosts do NOT fix running containers."
echo "- Audit statically linked curl copies: find / -type f -name 'curl' -exec sh -c '{} --version 2>/dev/null' \;"