CVE-2026-64940: Tegalog Authentication Bypass Vulnerability

CVE-2026-64940 Overview

CVE-2026-64940 is an authentication bypass vulnerability in Tegalog -Fumy Otegaru Memo Logger-, a web-based memo logging application provided by Nishishi Factory. The flaw stems from a permissive regular expression used during authentication, which allows an attacker with network access to log in to the management console without valid credentials. Once authenticated, the attacker gains access to any operation exposed through the management interface. The issue is tracked under [CWE-625: Permissive Regular Expression]. External details are available in the JVN Security Advisory and the vendor Nishishi Notice Announcement.

Critical Impact
An unauthenticated network attacker can log in to the Tegalog management console and perform any administrative action available through it.

Affected Products

Tegalog -Fumy Otegaru Memo Logger- (Nishishi Factory)
Deployments exposing the Tegalog management console to network-reachable clients
Web hosting environments running vulnerable Tegalog releases prior to the vendor fix

Discovery Timeline

2026-08-10 - CVE-2026-64940 published to NVD
2026-08-10 - Last updated in NVD database

Technical Details for CVE-2026-64940

Vulnerability Analysis

The vulnerability resides in the login validation logic of the Tegalog management console. Authentication relies on a regular expression that is too permissive to correctly enforce credential matching. As a result, crafted inputs can satisfy the regex check even when they do not correspond to the expected password value.

Because the flaw is exploitable over the network without authentication or user interaction, any attacker who can reach the management console URL can attempt the bypass. Successful exploitation yields full management-console privileges, including modification of stored memos, configuration changes, and any other actions the console exposes. The primary impact is to integrity, with secondary impact to confidentiality and availability of the hosted content.

Root Cause

The root cause is an improperly constrained regular expression used in credential validation, categorized under [CWE-625: Permissive Regular Expression for File Name or Path]. Regex patterns that omit strict anchors or use overly broad character classes can match inputs the developer did not intend to accept. In authentication paths, this transforms a comparison intended to be exact into a partial or pattern-based match that attackers can satisfy trivially.

Attack Vector

The attack vector is network-based and unauthenticated. An attacker submits a crafted authentication request to the Tegalog management console endpoint. The permissive regex accepts the crafted value as a valid credential and issues a management session. No prior access, tokens, or user interaction are required. See the JVN Security Advisory for coordinated disclosure details.

No verified public proof-of-concept code is available at time of writing. The vulnerability mechanism is a logic flaw in credential regex validation rather than a memory-corruption or injection primitive, so exploitation requires only a standard HTTP client.

Detection Methods for CVE-2026-64940

Indicators of Compromise

Successful management console logins from unexpected source IP addresses or geographies
Unrecognized administrative actions in Tegalog logs, including memo modifications, deletions, or configuration edits
Authentication requests containing unusual or malformed credential fields that still result in a valid session
New or altered files in the Tegalog installation directory that were not produced by legitimate administrators

Detection Strategies

Review Tegalog access and application logs for management-console requests that lack a preceding legitimate authentication pattern
Alert on multiple login attempts from a single source followed by a successful login to the console
Compare current Tegalog configuration and stored memo content against known-good baselines to identify unauthorized changes

Monitoring Recommendations

Forward web server and Tegalog application logs to a centralized log platform and retain them for post-incident analysis
Monitor for outbound connections initiated by the web host after a management-console login, which may indicate follow-on abuse
Track administrative endpoint traffic volume and alert on anomalous spikes correlated with the disclosure date

How to Mitigate CVE-2026-64940

Immediate Actions Required

Restrict network access to the Tegalog management console using IP allow-lists, VPN, or HTTP authentication at the web-server layer
Rotate all Tegalog administrator credentials after applying the vendor fix
Audit stored memos and configuration for unauthorized modifications made prior to remediation

Patch Information

Nishishi Factory has published remediation guidance in the vendor Nishishi Notice Announcement. Administrators should upgrade to the fixed Tegalog release identified in that notice and in the coordinated JVN Security Advisory. Verify the running version after upgrade and confirm the corrected authentication logic is in place.

Workarounds

Place the management console behind a reverse proxy that enforces HTTP Basic or Digest authentication as a second factor
Block access to the management-console path at the web server or WAF layer for all non-administrative source IPs
Temporarily disable the management console when it is not actively required for administration

bash

# Example: restrict Tegalog admin path in Apache to trusted IPs
<Location "/tegalog/admin">
    Require ip 203.0.113.0/24
    Require ip 198.51.100.42
</Location>