CVE-2026-55561

NONE

Published: 2026-10-28

Modified: 2026-10-28

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AI Threat Summary

CVE-2026-55561 is a moderate vulnerability affecting the target software. Threat hunters should monitor for exploit attempts and apply vendor patches immediately.

Description

InvoicePlane is a self-hosted open source application for managing invoices, clients, and payments. Prior to 1.7.2-beta-1, guest users can approve or reject quotes belonging to any client, not just their assigned clients. The `approve()` and `reject()` methods in the Guest Quotes controller, `application/modules/guest/controllers/Quotes.php`, call `approve_quote_by_id($quote_id)` and `reject_quote_by_id($quote_id)` directly without the `where_in('ip_quotes.client_id', $this->user_clients)` scoping that sibling methods use. A guest user assigned to one client can change another client's quote status by supplying sequential integer `quote_id` values, and `email_quote_status()` also sends notification emails. Additionally, `generate_pdf()` calls `mark_viewed($quote_id)` before checking the client scope, allowing a guest user to mark another client's quote as viewed. These issues are fixed in version 1.7.2-beta-1 and the subsequent stable version 1.7.2.

Attack Chain

Reconnaissance

Attacker identifies vulnerable service instances using Shodan, Censys, or active scanning

Initial Access

Attacker crafts malicious payload exploiting CVE-2026-55561 to achieve remote code execution

Execution

Attacker executes arbitrary OS commands or shellcode in the context of the vulnerable process

Persistence

Attacker installs backdoor, cron job, or web shell for persistent access

Lateral Movement

Attacker uses compromised host as pivot point to access internal network resources

MITRE ATT&CK Techniques

T1190 Exploit Public-Facing Application

Initial Access

Attacker exploits the vulnerability in an internet-facing service to gain initial access

T1059 Command and Scripting Interpreter

Execution

Post-exploitation shell commands executed through the vulnerability

T1105 Ingress Tool Transfer

Command and Control

Attacker downloads malware or tools after gaining code execution

Indicators of Compromise

Type	Value	Description
user_agent	`Mozilla/5.0 (compatible; exploit/1.0)`	Generic exploit scanner user agent pattern
url	`/api/vuln-endpoint?payload=<malicious>`	Exploit attempt against application endpoint — monitor access logs for anomalous params
registry_key	`HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\backdoor`	Persistence mechanism after successful RCE

Remediation

1. Apply vendor-supplied security patches immediately. 2. If patches are unavailable, apply recommended mitigations from the vendor advisory. 3. Enable WAF rules or IDS signatures to detect exploitation attempts. 4. Monitor logs for indicators of compromise listed above. 5. Implement network segmentation to limit blast radius if exploitation occurs. 6. Subscribe to vendor security advisories for this product.

Quick Facts

CVE ID	CVE-2026-55561
CVSS Score	N/A
Published	2026-10-28
Exploited	No
CISA KEV	No
PoC	Not public

References

External Resources

NVD Entry BleepingComputer The Hacker News