CVE-2026-58224

Executive Summary

CVE-2026-58224 is an integrity-validation and bounds-checking flaw in Samba's CTDB (Clustered TDB) clustered database service. An attacker with access to the CTDB private network can transmit malformed protocol packets containing invalid field lengths, improperly terminated strings, or inconsistent packet sizes; the receiving node parses these packets without adequate validation, leading to process crashes, excessive memory consumption, and — in limited cases — disclosure of adjacent memory contents. Clustered Samba deployments (file servers and Samba-based Active Directory domain controllers) are the affected population; the vulnerability is rated CVSS 6.5 (medium) with a high availability impact, and no public exploit or in-the-wild activity has been confirmed as of this report.

Technical Analysis

Samba's CTDB provides clustered database semantics for Samba environments, synchronizing TDB (Trivial Database) data across multiple cluster nodes over a dedicated private interconnect. The CTDB protocol operates under an implicit trust model: only well-formed packets from peer cluster nodes are expected on that network, and the protocol lacks cryptographic or structural integrity verification of received data. This maps directly to CWE-353 (Missing Support for Integrity Check), where the receiving parser does not mandate — or correctly perform — integrity checks on incoming protocol data before acting on attacker-influenced values inside those packets.

The NVD description identifies three specific malformed-packet conditions that trigger the flaw:

1. Invalid field lengths — a declared length value inside a packet field does not match the actual size of the accompanying data. Without bounds validation, the parser trusts these values for buffer operations, potentially causing out-of-bounds reads or writes.
2. Improperly terminated strings — string fields are processed on the assumption that they are NUL-terminated. A packet lacking the expected terminator causes the parser to read past the end of the packet buffer, producing an out-of-bounds read that can crash the process or leak adjacent memory.
3. Inconsistent packet sizes — the total packet size is inconsistent with the sum of its internal fields. The parser may read beyond the actual packet boundary or allocate memory based on an inflated declared size.

The result of processing these malformed packets is threefold: (a) process crashes from out-of-bounds access, (b) excessive memory consumption when attacker-controlled length values drive large allocations, and (c) limited adjacent-memory disclosure from out-of-bounds reads of heap or stack memory adjacent to the packet buffer.

Attack surface. The vulnerable listener is bound to the CTDB private network — the dedicated cluster interconnect that in standard Samba deployments uses a distinct TCP listener (commonly port 4379 by default configuration; verify against your deployment documentation). The CVSS vector (AV:A) confirms that an attacker must already be positioned on the same adjacent network segment as the CTDB cluster — for example, a compromised non-cluster host on the cluster VLAN, or a host on shared backplane infrastructure. No authentication is required (PR:N) and no user interaction is needed (UI:N). The scope is unchanged (S:U); confidentiality and integrity impacts are rated none in the CVSS vector, while availability is rated high — reflecting the primary DoS character of the flaw, with the memory-disclosure aspect treated as limited and secondary.

Patch status. Patch confidence is 3/4 (LIKELY), with the Debian security tracker independently confirming a fix. Affected version ranges and an upstream vendor advisory were not available in the NVD/CNA data at the time of writing, so operators must track the Debian packaging and upstream Samba release notes for the exact fixed versions.

Exploitation Scenarios

No public proof-of-concept, Nuclei template, or exploit code has been identified for CVE-2026-58224. The attack chain below is inferred from the vulnerability class (missing integrity and bounds checks in a binary protocol parser) and the NVD description. Specific function names, packet field names, and exact payload layouts are not disclosed in the available data and are therefore not asserted.

1. Reconnaissance / target identification. The attacker must first gain a foothold on the CTDB private network segment (CVSS adjacency requirement). From there, they scan the segment for the CTDB listener — for example, TCP connect scans toward the default CTDB port across cluster subnets, or passive traffic observation to learn cluster node addresses and packet patterns.

2. Triggering the flaw. The attacker crafts CTDB protocol packets that violate integrity expectations: field length values that exceed the actual enclosed data, string fields without NUL terminators, or a declared total packet length inconsistent with the payload actually transmitted. Because the receiving parser performs inadequate bounds and integrity checks, these packets are accepted for processing rather than rejected as malformed.

3. Payload / execution method (vulnerability-class level). Delivery is a direct packet injection to the CTDB listener over the private network. No authentication is required beyond network access, so every crafted packet is parsed. The lack of bounds checking turns attacker-controlled length/termination values into out-of-bounds read or write conditions, or drives oversized memory allocations. There is no indication of remote code execution; the expected outcomes are process crashes (via invalid memory access) and memory exhaustion (via repeated large allocations).

4. Post-exploitation impact. A crashed or memory-exhausted CTDB node loses its role in the clustered database. Samba services on that node that depend on CTDB — such as cluster file locking, share state, and Samba AD DC database synchronization — become unavailable or force failover. Repeated packet injection produces a sustained denial of service across the cluster. The limited out-of-bounds read path may, in isolated cases, return adjacent memory contents to the attacker, although the CVSS scoring treats this as negligible for confidentiality.

Impact Assessment

Business impact. Organizations running clustered Samba configurations are directly affected. Clustered Samba file servers and Samba-based Active Directory domain controllers depend on CTDB for consistent database state, locking, and node coordination. Denial of service against a CTDB node translates into interrupted file services, authentication failures, and cluster failover storms. In environments where Samba provides core file or identity services, even a partial cluster outage carries significant operational cost.

Affected systems. Samba installations that enable and expose CTDB on a private network. Standalone, non-clustered Samba deployments that do not run the CTDB service are not exposed to this attack surface.

Blast radius and severity context. CVSS 3.1 score is 6.5 (medium), with the vector CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. The availability subscore dominates; the attack requires adjacent network access, which materially reduces remote-exposure risk. The EPSS score is 0.00405 (33.7th percentile of exploited CVEs), indicating low current threat-actor interest. The CVE is not listed in CISA's Known Exploited Vulnerabilities catalog, and no evidence of exploitation in the wild has been reported. Business impact should still be treated as significant in Samba cluster environments because the availability impact is high and the exploit is trivial in principle once network adjacency exists.

Detection Guidance

Detection should focus on three observable phenomena: (1) anomalous access to the CTDB private network listener, (2) heuristic wire-level signs of malformed CTDB packets, and (3) crash or memory-exhaustion events on CTDB nodes. All thresholds and IP lists below must be adjusted to local cluster topology. The default CTDB listener port used in the rules is the commonly-deployed value 4379 — confirm against your environment.

Sigma Rule

title: Suspicious Access to Samba CTDB Private Network Listener
id: 7d3a2f8e-1c4b-4a9e-8d5a-2c6e9f0b3a51
status: experimental
description: Detects inbound connections to the Samba CTDB listener port from source addresses outside the trusted cluster private subnets. May indicate reconnaissance or packet-injection activity targeting CVE-2026-58224.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-58224
  - https://security-tracker.debian.org/tracker/CVE-2026-58224
author: Valters IT Threat Intelligence
date: 2026/05/26
logsource:
  category: network_connection
  product: firewall
detection:
  selection:
    destination.port: 4379
  filter_cluster_peers:
    source.ip:
      - 10.10.20.0/24      # Replace with actual CTDB private network
      - 192.168.50.0/24    # Replace with actual CTDB private network
  condition: selection and not filter_cluster_peers
falsepositives:
  - New cluster node provisioning on the CTDB private network
  - Administrative access from management hosts (extend filter as required)
level: medium
tags:
  - attack.t1499
  - cve.2026-58224

YARA Rule

/*
   Heuristic YARA rule for CVE-2026-58224.
   Targets captured CTDB protocol traffic (e.g., packet captures or
   pcap-extracted TCP streams) and CTDB process memory dumps.

   NOTE: The CTDB wire format differs across Samba releases. Validate
   length-field offsets against the CTDB protocol header definitions for
   your deployment before operational use. This rule flags implausible
   length patterns and protocol identifiers, not confirmed exploits.
*/
rule cve_2026_58224_ctdb_malformed_packet_heuristic
{
    meta:
        author      = "Valters IT Threat Intelligence"
        description = "Heuristic detection of CTDB protocol packets with implausible length fields consistent with CVE-2026-58224 malformed packet handling"
        cve         = "CVE-2026-58224"
        score       = 60

    strings:
        $ctdb_ref = "ctdb" ascii nocase
        $len_max  = { FF FF FF FF }   // absurd length value (e.g., 0xFFFFFFFF)
        $len_neg  = { FF FF 00 00 }   // length value inconsistent with small packet
        $trunc    = { 00 00 00 00 }   // zero-length field preceding non-empty data

    condition:
        $ctdb_ref and any of ($len_max, $len_neg, $trunc)
}

Suricata IDS Rule

# Rule 1 — Truncated/anomalously short TCP payloads to the CTDB listener.
# Heuristic: legitimate CTDB protocol exchange requires a minimum structured
# header; payloads smaller than ~16 bytes are suspicious and may trigger the
# inconsistent-size / unterminated-string path of CVE-2026-58224.
alert tcp any any -> any 4379 (msg:"CVE-2026-58224 Potential malformed CTDB packet (short segment)"; flow:to_server; dsize:1:16; reference:cve,2026-58224; classtype:attempted-dos; sid:2026582201; rev:1;)

# Rule 2 — Flood / connection-request pattern toward the CTDB listener from a
# single source, consistent with repeated malformed-packet injection or
# memory-exhaustion attempts.
alert tcp any any -> any 4379 (msg:"CVE-2026-58224 Possible CTDB DoS packet flood from single source"; flow:to_server; flags:S; threshold:type both, track by_src, count 50, seconds 60; reference:cve,2026-58224; classtype:attempted-dos; sid:2026582202; rev:1;)

Elastic Detection

// EQL query — detect inbound connection activity against the CTDB listener
// that exceeds normal cluster peer behavior. Adjust thresholds to cluster size.
network where destination.port == 4379 and network.direction == "inbound"
| stats connection_attempts = count(), source_count = cardinalize(source.ip) by destination.ip
| where connection_attempts > 50 or source_count > 5

Splunk SPL Query

# Query 1 — network/firewall telemetry: anomalous connection volume to the CTDB listener
index=netflow dest_port=4379
| stats count AS attempts, dc(src_ip) AS unique_sources BY dest_ip
| where attempts > 100 OR unique_sources > 10
| eval cve="CVE-2026-58224", confidence="medium"

# Query 2 — host syslog: CTDB node crash or malformed-packet error indicators
index=os sourcetype=syslog (program=ctdb OR program=ctdbd) ("corrupt" OR "segfault" OR "core dumped" OR "invalid" OR "packet size" OR "out of memory")
| stats count BY host, program, source, _time
| sort - _time

Wazuh OSSEC Rule

<!-- Place in the local ruleset (e.g., /var/ossec/etc/rules/local_rules.xml)
     and restart the Wazuh manager. Adjust the program_name to match the
     actual CTDB logging source name in your environment ("ctdb", "ctdbd",
     or the Samba log tag used on your cluster nodes). -->
<group name="samba,ctdb,">
  <rule id="100512" level="10" frequency="8" timeframe="300">
    <decoded_as>syslog</decoded_as>
    <program_name>ctdb</program_name>
    <regex>corrupt|invalid length|packet size|segfault|core dumped|out of memory</regex>
    <description>CVE-2026-58224: repeated malformed CTDB traffic or process crash on Samba cluster node</description>
    <mitre>
      <id>T1499</id>
    </mitre>
    <group>cve-2026-58224,denial_of_service,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence is 3/4 (LIKELY), with two independent sources confirming a fix; the known patch source is Debian. The exact upstream fixed version was not published in the NVD/CNA data, so validate package versions against upstream Samba release notes and the Debian security tracker.

1. Immediate mitigations.

   • Restrict access to the CTDB private network at the network layer. Use dedicated VLANs and ACLs so only cluster peer nodes can reach the CTDB listener. Treat the private network as hostile-capable — do not rely on physical or logical separation alone.
   • Deploy host-based firewall rules on each cluster node allowing the CTDB listener port only from verified peer node IPs.
   • If clustering is not actively required in a given Samba deployment, disable the CTDB service entirely to remove the attack surface.
   • Monitor connections to the CTDB listener and CTDB node health (crash/restart events) until patching is complete.

2. Patch / upgrade steps.

   • Track and apply the updated Samba packages from the Debian security tracker for CVE-2026-58224.
   • Vendors not using Debian packaging should consult the upstream Samba security announcement and apply the corresponding fixed CTDB release once published; the vendor advisory was not yet available in the NVD/CNA data at the time of this report.
   • Test the patched packages in a staging cluster prior to production rollout to verify cluster failover behavior is unaffected.

3. Long-term hardening.

   • Apply least-privilege network architecture: separate the CTDB private interconnect from general corporate traffic with strict egress/ingress filtering.
   • Where supported by the protocol version and deployment constraints, add cryptographic integrity and/or encryption to the CTDB private interconnect to raise the bar for packet injection and tampering.
   • Add the CTDB protocol parser to an ongoing fuzzing program; this vulnerability class (missing integrity checks plus inadequate bounds validation) is well suited to fuzz-driven discovery during development.
   • Enable automated crash detection and restart policies for CTDB daemons, and feed crash telemetry into the SIEM for correlation.

References

• NVD — CVE-2026-58224: https://nvd.nist.gov/vuln/detail/CVE-2026-58224
• Debian Security Tracker — CVE-2026-58224: https://security-tracker.debian.org/tracker/CVE-2026-58224
• MITRE CWE-353 (Missing Support for Integrity Check): https://cwe.mitre.org/data/definitions/353.html
• Samba Security Announcements: https://www.samba.org/samba/security/
• CISA Known Exploited Vulnerabilities Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog (CVE-2026-58224 is not currently listed)

No known threat actor campaigns or exploit-in-the-wild evidence are associated with CVE-2026-58224 as of this report. The EPSS score (0.00405, 33.7th percentile) and the absence of public PoC code indicate low immediate exploitation likelihood, but the vulnerability is trivially reachable by any host with access to the CTDB private network and should be patched on the normal security maintenance cycle, with priority in actively clustered Samba environments.