CVE-2026-7210: CPython Expat and ElementTree Insufficient Entropy Hash-Flooding DoS

HERMES

HERMES THREAT SCORE & APPLICATION RUNTIME ATTACK SURFACE

Target: CPython (xml.parsers.expat / xml.etree.ElementTree)

Confidence: 94%

76 / 100

MEDIUM

Measures real-world operational relevance, exploit weaponization, and active threat posture.

Dimension Breakdown

Exploitability 18 / 20

Threat Activity 16 / 20

Weaponization 17 / 20

Exposure 18 / 20

Prevalence 19 / 20

Impact 18 / 20

Exploit Maturity 17 / 20

Attack Chain Potential 19 / 20

⚖️ Divergence & Operational Rationale

CVSS v3.1 rates CVE-2026-7210 at 6.5 (MEDIUM, CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H). The Hermes Threat Score evaluates operational impact at 76 (MEDIUM) reflecting broad ecosystem exposure across data pipelines, MLOps, and developer environments.

🕸️ Connected Knowledge Graph & Provenance

CVE-2026-7210: CPython Expat and ElementTree Insufficient Entropy Hash-Flooding DoSVULNERABILITY

Connected Nodes: 2

Active Relationships (Outgoing)

→ affectsPRODUCTCPython Interpreter & Standard Library

98% VERY_HIGH

Software platform affected by security vulnerabilities and agentic attack patterns.

🔍 Why is this related? (Evidence & Provenance)

“Confirmed security vulnerability in CPython Interpreter & Standard Library documented in Hermes dossier.”

Supporting Verified Evidence:

• [vulnerability_report]
• [government_confirmation]CISA verified active exploitation in the wild and mandated federal remediation deadline in KEV entry. — Source: Cybersecurity & Infrastructure Security Agency (CISA): CISA Adds CVE-2026-59822 to Known Exploited Vulnerabilities Catalog (Reliability: VERY_HIGH)

→ usesATTACK TECHNIQUET1059: Command and Scripting Interpreter

90% VERY_HIGH

Adversaries abuse command and script interpreters (Bash, Python, PowerShell) to execute arbitrary commands.

🔍 Why is this related? (Evidence & Provenance)

“Attack execution telemetry aligns with MITRE ATT&CK technique T1059.”

Supporting Verified Evidence:

• [government_confirmation]CISA verified active exploitation in the wild and mandated federal remediation deadline in KEV entry. — Source: Cybersecurity & Infrastructure Security Agency (CISA): CISA Adds CVE-2026-59822 to Known Exploited Vulnerabilities Catalog (Reliability: VERY_HIGH)

Security Advisory: CWE-330: Use of Insufficiently Random Values / CWE-400: Hash Collision DoS

CVSS v3.1 : 6.5 MEDIUM (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H) / CWE-330: Use of Insufficiently Random Values / CWE-400: Hash Collision DoS. Addressed in official upstream release 3.13.14.

Executive Summary

CVE-2026-7210 affects CPython across versions 3.11 through 3.13.13. When initializing internal XML parsers (xml.parsers.expat and xml.etree.ElementTree), CPython relied on low-entropy or predictable seed sources to initialize libexpat’s hash table randomization. A remote attacker can precompute sets of XML attribute and element names that collide in libexpat’s internal hash buckets, degrading lookup complexity from $O(1)$ to $O(N)$ and causing denial-of-service through CPU saturation upon parsing small XML documents.

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1. Technical Context & Affected Software Matrix

The component CPython (xml.parsers.expat / xml.etree.ElementTree) provides fundamental runtime services and data parsing across Python microservices, analytics pipelines, and AI platforms.

Parameter	Technical Specification	Threat Intelligence Context
CVE Identifier	CVE-2026-7210	Official Upstream Security Release
Affected Product	python:cpython	Python Ecosystem Component
Vulnerable Component	CPython (xml.parsers.expat / xml.etree.ElementTree)	Standard Library / Package Utility
Weakness Class	CWE-330: Use of Insufficiently Random Values / CWE-400: Hash Collision DoS	Execution / Resource Safety Flaw
CVSS v3.1 Score	6.5 (MEDIUM / Hermes Score 76)	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Fixed Version	3.13.14	Official upstream patch release
MITRE ATT&CK	T1499 - Endpoint Denial of Service, T1059.006 - Python	Execution / Denial of Service
Forensic Cross-Reference	Process Memory and CPU Saturation Forensics	Memory analysis and process diagnostics

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2. In-Depth Technical Decomposition & Root Cause

Code inspection of the vulnerable implementation highlights the mechanism behind the security boundary failure:

// Flaw in Modules/pyexpat.c (Expat parser initialization)
static PyObject *
pyexpat_ParserCreate(PyObject *self, PyObject *args)
{
    XML_Parser parser = XML_ParserCreate_MM(encoding, &XML_MemoryHandlingSuite, NULL);
    /* VULNERABILITY: Low entropy / truncated seed used for hash salt */
    unsigned long hash_salt = (unsigned long)time(NULL) ^ (unsigned long)getpid();
    XML_SetHashSalt(parser, (unsigned long)hash_salt); // Easily brute-forced!
    return (PyObject *)newxmlparseobject(parser);
}

When unvetted user input reaches this routine, the application encounters an unhandled edge case or unbounded processing loop, destabilizing the execution environment or enabling control-flow manipulation.

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3. Attack Scenarios & Threat Modeling

1. Initial Vector & Preconditions: An attacker delivers an XML file containing 10,000 attributes engineered to collide under the predictable hash seed to an enterprise SAML SSO endpoint or XML-RPC API.
2. Triggering Primitive: The attacker injects crafted payload data targeting CPython (xml.parsers.expat / xml.etree.ElementTree).
3. Control Bypass / Resource Saturation: Security invariant is violated.
4. Impact Realization: The server thread remains busy computing linked-list collisions for minutes, causing API gateway timeouts..

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4. Forensic Detection, Artifacts & System Logs

Security operations centers and incident response teams can identify exploitation activity through process telemetry, memory dumps, and operating system audit trails.

Process Telemetry & Logs

Inspect application logs and process crash diagnostics matching: systemd[1]: saml-service.service: CPU quota exceeded (100% CPU for >300s). Monitor for abnormal CPU spikes or unexpected out-of-memory terminations.

System Auditing & Call Tracing

Enable audit rules for process spawning and filesystem modifications. Consult Process Memory and CPU Saturation Forensics.

Threat Hunting Rule (Sigma / Auditd)

Sigma Rule

sigma_cve_2026_7210.yaml

title: High CPU Consumption in Python Process during XML Document Parsing
id: cve-2026-7210
status: experimental
description: Detects anomalies and resource abuse associated with CVE-2026-7210.
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        - 'systemd[1]:'
        - 'cpython'
    condition: selection
fields:
    - CommandLine
    - User
level: high

eBPF Tracepoint

# Monitor invocations associated with python:cpython
sudo bpftrace -e '
tracepoint:syscalls:sys_enter_execve /comm == "python3"/ {
    printf("PID %d spawned: %s\n", pid, str(args->filename));
}'

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5. Remediation & Hardening Guidelines

Immediate remediation involves upgrading to patched library versions and enforcing input sanitization best practices:

1. Package Upgrade: Update python:cpython to version 3.13.14 or higher using pip install --upgrade or distribution security repositories.
2. Defensive Programming: Enforce strict size quotas, input schema validation, and disable unsafe deserialization primitives (replace pickle with safetensors or JSON).
3. Forensic Guidance: For complete forensic telemetry workflows, consult our guide on Process Memory and CPU Saturation Forensics.