CVE-2026-81838

Executive Summary

CVE-2026-81838 is a relative path traversal vulnerability (CWE-23) affecting the ZIP extraction functionality of AWS Diagram As Code (awsdac), an Amazon-maintained open-source tool used to define cloud infrastructure diagrams as code. Versions 0.10 through 0.23 are vulnerable. Successful exploitation allows a third party to write arbitrary files to the local filesystem by supplying a crafted diagram bundle containing ZIP entries with path traversal sequences (e.g., ../../). The CVSS score is 7.1 (High), reflecting high impact to file integrity and availability with low attack complexity — though exploitation requires user interaction (e.g., opening a malicious bundle) and is local in nature. Users should upgrade to version 0.24 or later to remediate.

Technical Analysis

The vulnerability resides in the ZIP extraction logic within awsdac. When the tool processes a "diagram bundle" — an archive that packages diagram assets — the extraction routine fails to sanitize or validate entry names against path traversal sequences prior to writing files to disk. Crafted ZIP entry names containing relative path constructs (e.g., ../../../../tmp/evil.sh) cause the extraction to write files outside the intended destination directory.

Vulnerability Class: Relative Path Traversal (CWE-23). This differs from absolute path traversal (CWE-22) in that the attacker leverages relative navigation sequences to escape the extraction root directory rather than supplying absolute paths. The class is fundamentally a failure to validate or canonicalize input paths before filesystem operations.

Attack Surface: The vulnerable code path executes when a user opens or imports a diagram bundle in awsdac. The bundle is parsed and ZIP entries are extracted. Because the awsdac tool is typically run locally by developers or cloud architects, the attack surface is the local environment of the user who processes untrusted bundles. No network service is implicated; the attack vector is AV:L (Local).

Technical Mechanism (at class level): ZIP archives store entry names as strings. A secure extraction routine must (a) reject or sanitize entry names containing . or .. components, or (b) validate the canonicalized destination path begins with the target extraction directory. The vulnerable implementation presumably performs the extraction using the attacker-supplied entry name directly, without canonicalization, allowing the ../ sequence to navigate the filesystem during the write operation.

Impact Dimensions per CVSS: The vector string CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H indicates:

• Integrity (I:H): Arbitrary file content can be written to any user-writable location, allowing overwrite of configuration files, scripts, or other assets.
• Availability (A:H): Overwriting critical files can render the system or applications non-functional.
• Confidentiality (C:N): No direct data disclosure mechanism.
• User Interaction (UI:R): The victim must open/process a crafted bundle.
• Privileges Required (PR:N): No pre-existing access or elevated privileges required beyond local user context.
• Scope (S:U): Impact is confined to the vulnerable component's security scope.

Insufficient technical detail is available in the NVD description to identify specific function names, code locations, or class structures within the awsdac codebase.

Exploitation Scenarios

No public PoC exists (POC_STATUS: None). The attack chain below is inferred from the vulnerability class and NVD description — not from observed exploit activity.

Step 1 — Reconnaissance/Target Identification: The attacker identifies the target's use of awsdac (versions 0.10–0.23). This may be achieved via job postings on LinkedIn, GitHub repositories that reference awsdac in CI/CD pipelines, package manifests, or developer configuration files inadvertently exposed. The attacker does not require network acess to the target; the delivery vector is social engineering or supply-chain style distribution (e.g., sharing a "diagram template" in a community forum, chat group, or via email).

Step 2 — Trigger the Flaw: The attacker crafts a malicious ZIP archive (a diagram bundle) containing legitimate-looking diagram files (JSON/YAML definitions, PNG/PDF assets) alongside at least one ZIP entry with a path traversal name, e.g., ../../.bashrc or ../../../../etc/cron.d/malicious. The bundle is delivered to the victim and — because UI:R is required — the victim must open it in awsdac. The awsdac parsing process reads the ZIP manifest and enqueues entries for extraction.

Step 3 — Payload Execution Mechanism (vulnerability-class level): During extraction, the vulnerable routine resolves the destination file path by concatenating the extraction directory with the ZIP entry name without sanitization. The relative traversal components (../) cause the operating system to resolve the path outside the intended extraction directory. The payload file content (attacker-embedded bytes) is written to the resolved arbitrary path. No code execution occurs at this stage — the primitive is arbitrary file write with attacker-controlled content at attacker-chosen (user-writable) paths.

Step 4 — Post-Exploitation Impact: Once arbitrary file write is achieved, the attacker's capability depends on what the victim user can write to:

• Overwrite user dotfiles (.bashrc, .bash_profile, .zshrc) to inject malicious commands executed at next shell start.
• Plant files in autostart directories (e.g., ~/.config/autostart/) for GUI session persistence.
• Overwrite application configuration files that awsdac (or sibling tools) reads at next run, redirecting logic to attacker-controlled content.
• Overwrite cron job definitions if the user has crontab write permissions.
• Target project source files: overwriting source files in developer repositories could inject malicious code that enters the CI/CD supply chain.
• Denial of service: overwriting critical files with corrupt/empty content renders dependent functionality inoperative (A:H).

The high availability impact (A:H) is consistent with destructive overwrites, while high integrity impact (I:H) supports the persistence/code-injection scenario. Note the scope is Unchanged (S:U) — the attacker cannot escape the user's privilege boundary, but within that boundary the write primitive is largely unconstrained.

Impact Assessment

Business Impact: For organizations using awsdac to manage cloud architecture diagrams and infrastructure-as-code assets, a successful attack could result in:

• Local persistence: Attacker-controlled commands executing in the context of developers, cloud architects, or CI runners using awsdac.
• Supply-chain poisoning: If a diagram artifact repository is poisoned with a malicious bundle that other engineers download and open, the attack scales across the organization.
• Availability loss: Overwriting critical local configuration or build files disrupts development workflows and CI pipeline reliability.
• Data integrity: Diagram assets, source code, and configuration could be silently modified, and because integrity violations are subtle, malicious modifications may persist unnoticed.

Affected Systems: All installations of awsdac versions 0.10 through 0.23 inclusive. The tool is typically used in developer workstations and CI environments. The OSV package entry references a specific code tree (7bf6274edc5035f286a45b6282bdaa78d8c3298a), indicating the fix commit is identified but unfixed states are tracked.

Blast Radius: The vulnerability is local-only (AV:L) and requires user interaction. However, because awsdac bundles may be exchanged as templates or shared artifacts, the blast radius from a single malicious bundle is any team member or CI builder that processes it. EPSS score of 0.00134 (3.2nd percentile) indicates very low observed exploitation likelihood at time of assessment, and the CVE is not listed in CISA's Known Exploited Vulnerabilities catalog.

CVSS Subscore Interpretation: The severity (7.1) is driven by the Integrity and Availability subscores (both High). Confidentiality of the target system is not directly impacted; however, the arbitrary file write capability can be leveraged into arbitrary code execution through OS-level mechanisms (e.g., writing to profile files), at which point confidentiality impact would follow — but this is beyond the vulnerability's declared scope.

Detection Guidance

The following detection rules target post-exploitation artifacts and attempt to detect the execution phase of the attack. Because awsdac processing occurs locally and the malicious action is the extraction of path traversal names, network-based detection (Suricata) is minimally effective unless the bundle is fetched across monitored network boundaries. The rules below therefore focus on filesystem-level and process-level telemetry.

Sigma Rule

title: AWS Diagram as Code - Path Traversal Attempt via Zip Extraction
id: c9f3d2a1-7b5e-4c3a-9f1e-2d4b6c8a0e5f
status: experimental
description: Detects process execution of awsdac (diagram-as-code) reading a zip archive whose member names contain path traversal sequences, indicative of CVE-2026-81838 exploitation attempts.
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2026-81838
tags:
    - attack.t1204
    - attack.initial-access
    - cve.2026.81838
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith:
            - '/awsdac'
            - '/diagram-as-code'
        CommandLine|contains:
            - '.zip'
            - '.bundle'
    filter_legit:
        CommandLine|contains:
            - 'extract'
            - 'sync'
    condition: selection and not filter_legit
fields:
    - Image
    - CommandLine
    - User
falsepositives:
    - Legitimate bundle processing operations by authorized users
level: medium

YARA Rule

rule CVE_2026_81838_Zip_Traversal_Payload
{
    meta:
        author = "Valtersit Cyber Threat Intelligence"
        description = "Detects ZIP archives or diagram bundles containing entry names with relative path traversal sequences, candidates for CVE-2026-81838 exploitation payloads"
        cve = "CVE-2026-81838"
        date = "2026-01-01"
        severity = "high"
    strings:
        $zip_sig = { 50 4B 03 04 } // PK\x03\x04 - local file header
        $traversal_1 = "../../"
        $traversal_2 = "..\\..\\"
        $traversal_3 = /\.\.\/\.\.\/[A-Za-z0-9_\-\/]+/
        $awsdac_ref = "diagram" ascii nocase
    condition:
        $zip_sig at 0 and 2 of ($traversal_*) and any of ($awsdac_ref)
}

Note: YARA rules scan file contents. The above detects ZIP files (by PK header) that contain traversal sequences in their raw bytes. For live process-level detection, combine with process-monitoring rules.

Suricata IDS Rule

The attack is local-only; however, if diagram bundles transit the network (HTTP download, SMB share), the following rule detects zip file download with traversal-indicative content:

alert http any any -> any any (msg:"CVE-2026-81838 - Path Traversal Payload in Diagram Bundle Download"; flow:to_client,established; file.data; content:"PK"; depth:4; content:"../"; within:4096; fileext:"zip"; classtype:attempted-user; sid:202681838; rev:1;)

Caveat: Detection efficacy of payload-inspection rules is limited by HTTP body decompression and the fact that the zip binary structure may fragment traversal sequences across bounds. Network detection for CVE-2026-81838 is a secondary control; host-based detection is primary.

Elastic Detection

sequence by host.name, process.entity_id with maxspan=1m
  [process where event.action == "exec" and process.name : "*awsdac*"]
  [file where event.action in ("write", "overwrite") and 
     file.path : ("*\\..\\*", "*/../*") and
     file.path : ("/home/*", "C:\\Users\\*", "*/root/*")]

This EQL rule correlates an awsdac process execution followed by a file write containing parent-directory navigation components outside a standard extraction pattern — strong indicator of traversal-based write activity. Additional process event fields required: process.entity_id, file.path.

Splunk SPL Query

index=* sourcetype=linux_secure OR sourcetype=win_security
    earliest=-7d
| where process_name LIKE "%awsdac%" OR process_name LIKE "%diagram-as-code%"
| transaction process_id maxspan=60s
| search file_path="*../*" AND (file_path="/home/*" OR file_path="C:\\Users\\*" OR file_path="/root/*")
| stats count by host, user, process_name, file_path, _time
| sort - _time

Wazuh OSSEC Rule

<group name="local,">
  <rule id="100383" level="12">
    <if_sid>550</if_sid>
    <field name="file">\.\./</field>
    <description>CVE-2026-81838: awsdac process writing file with path traversal pattern</description>
    <group>pci_dss_11.4,</group>
  </rule>
</group>

Note on Wazuh rules: The above generic syscheck/audit rule detects any file modification containing ../ in reported paths; adjust if_sid to match your audit baseline rule. For correlated process-to-file SQL, use Wazuh's FIM capabilities auditing the home directories of users running awsdac.

Mitigation & Patch Guidance

Patch Confidence: 2/4 — CLAIMED. The only patch source is NVD, which states "users should upgrade to version 0.24 or later." This claim is not independently confirmed via vendor advisory or code repository inspection. Validate the availability and integrity of version 0.24 from the official awsdac repository (GitHub: awslabs/aws-diagram-as-code) and verify checksums.

Immediate Mitigations:

1. Do not open untrusted diagram bundles in awsdac. Treat any .zip, bundle, or archive arriving from unrecognized or non-trusted sources as potentially malicious, regardless of sender identity (social engineering may spoof trusted colleagues).
2. Inspect archive contents prior to processing: Before opening with awsdac, run unzip -l bundle.zip and review entry names. Reject archives containing ../, ..\, or absolute paths (/etc/, C:\) in any entry name.
3. Run awsdac under a sandboxed environment (Docker container, bwrap, Firejail) or with a restrictive umask and read-only bind mounts for sensitive directories, preventing writes outside an allowed extraction root even when exploitation occurs.
4. Restrict execution to non-privileged service accounts in CI environments — never run awsdac as root or with administrator privileges.

Patch/Upgrade Steps:

1. Upgrade awsdac to version 0.24 or later immediately — the disclosed remediation.
2. Verify the upgrade: awsdac --version or package manager query.
3. If version 0.24+ is confirmed on your package index, confirm the bundled extraction code performs canonicalization of all destination paths (resolving symlinks and normalizing ..).
4. If 0.24 is unavailable on your distribution's package manager, install from the official upstream GitHub release following the vendor's installation documentation.

Long-Term Hardening:

1. Adopt a vulnerability-management cadence for all open-source development tools; awsdac and similar utilities should be included in automated dependency scanning (OSV, SCA tools).
2. Establish bundle provenance: Maintain an internal registry of approved diagram bundles with cryptographic hashes; refuse bundles not matching the registry.
3. Segment CI environments from production data — limit blast radius of local-write primitives.
4. Monitor for CVE-2026-81838 appearing in CISA KEV — a KEV addition would elevate patch priority dramatically. As of this report: NOT in KEV.
5. Security awareness: Educate engineering teams on the risk of opening project files/templates from untrusted sources in local development tools.

References

1. NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2026-81838 — Official vulnerability description, CVSS vector, and patch statement (version 0.24 or later).
2. Vendor Repository (Patch Source): AWS Labs awsdac — GitHub repository (https://github.com/awslabs/aws-diagram-as-code (returned 404 — verify manually)). Validate release 0.24 availability and extraction code changes; note that vendor advisory is not yet independently confirmed per patch confidence 2/4.
3. OSV Package Tracker: OSV entry referencing code tree 7bf6274edc5035f286a45b6282bdaa78d8c3298a (vulnerable) — query at https://osv.dev/vulnerability/ for the associated OSV record.
4. MITRE CWE-23: https://cwe.mitre.org/data/definitions/23.html — Relative Path Traversal class description.
5. CISA KEV Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog — CVE-2026-81838 currently NOT listed; monitor for updates.

Campaign/Exploit-in-the-Wild Evidence: No known threat actor campaigns, public exploits, PoC code, or Nuclei templates exist for this CVE at the time of this report. EPSS probability of exploitation is 0.00134 (3.2nd percentile), indicating very low imminent exploitation likelihood. The CVE is not present in CISA's Known Exploited Vulnerabilities catalog. These search results are static assessments — revisit before prioritizing remediation.