CVE-2026-26747
Monicahq Monica 4.1.2
Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:NSummary
CVE-2026-26747 is a critical-severity Improper Neutralization of HTTP Headers for Scripting Syntax (CWE-644) vulnerability in Monicahq Monica. Its CVSS base score is 9.1 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Content Injection (T1659); ranked at the 32th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified map to SI-10 (Information Input Validation) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-26747 is a Host Header Poisoning vulnerability in Monica 4.1.2, stemming from improper handling of the HTTP Host header in the file app/Providers/AppServiceProvider.php. This issue is compounded by the default misconfiguration where the "app.force_url" setting is not defined and defaults to "false", causing the application to generate absolute URLs—such as those embedded in password reset emails—directly from the user-supplied Host header.
Remote attackers can exploit this vulnerability over the network (AV:N) with low attack complexity (AC:L), no privileges (PR:N), and no user interaction (UI:N), achieving high impacts on confidentiality (C:H) and integrity (I:H) without affecting availability (A:N). The CVSS v3.1 base score is 9.1, mapped to CWE-644. By poisoning the Host header in requests that trigger password reset emails, attackers can manipulate the links sent to victims, enabling account takeover or phishing via redirected reset URLs.
Mitigation details and further analysis are documented in the referenced advisory at https://github.com/hungnqdz/cve-research/blob/main/CVE-2026-26747.md, with the affected Monica repository available at https://github.com/monicahq/monica.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-7493
Vulnerability Data
A Host Header Poisoning vulnerability exists in Monica 4.1.2 due to improper handling of the HTTP Host header in app/Providers/AppServiceProvider.php, combined with the default misconfiguration where the "app.force_url" is not set and default is "false". The application generates absolute URLs…
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(such as those used in password reset emails) using the user-supplied Host header. This allows remote attackers to poison the password reset link sent to a victim,
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V4.2.3
Mitigating Controls (NIST 800-53 r5) AI
Input validation directly requires checking/neutralizing untrusted data such as HTTP headers before they reach browser components.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure SDLC practices directly require proper output encoding and header sanitization to prevent scripting injection.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing catches header-injection issues before release, covering most of the weakness.
Secure development lifecycle mandates input validation and output encoding that directly prevents header-injection flaws.
Application security requirements explicitly call for neutralizing untrusted data in HTTP headers.
Secure architecture principles reduce injection surfaces but do not prescribe header-specific controls.
Secure coding standards require proper escaping or rejection of scripting syntax in HTTP headers.