Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HSummary
CVE-2026-27641 is a critical-severity Improper Neutralization of Special Elements Used in a Template Engine (CWE-1336) vulnerability in Jugmac00 Flask-Reuploaded. Its CVSS base score is 9.8 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Template Injection (T1221); ranked in the top 39% of CVEs by exploit likelihood; 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 AC-3 (Access Enforcement) and SA-11 (Developer Testing and Evaluation) — 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.
Flask-Reuploaded, a file upload library for Flask applications, contains a critical path traversal and extension bypass vulnerability (CVE-2026-27641) affecting versions prior to 1.5.0. This flaw, linked to CWE-1336 and CWE-22, enables attackers to manipulate file paths and extensions during uploads, leading to arbitrary file writes and remote code execution via Server-Side Template Injection (SSTI). The vulnerability carries a CVSS v3.1 base score of 9.8, reflecting its high severity.
Remote, unauthenticated attackers can exploit this issue over the network with low complexity and no user interaction required. By crafting malicious filenames passed to the `name` parameter, they achieve arbitrary file writes on the server, potentially overwriting critical files, and escalate to RCE through SSTI when uploaded files are processed as templates.
The vulnerability has been patched in Flask-Reuploaded version 1.5.0, as detailed in the project's GitHub security advisory (GHSA-65mp-fq8v-56jr), pull request #180, and the fixing commit d64c6b2f71cb73734fc38baa0e3e156926361288. Workarounds include avoiding user input in the `name` parameter, relying solely on auto-generated filenames, and enforcing strict input validation if custom names are necessary.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-8616
Vulnerability Data
Flask-Reuploaded provides file uploads for Flask. A critical path traversal and extension bypass vulnerability in versions prior to 1.5.0 allows remote attackers to achieve arbitrary file write and remote code execution through Server-Side Template Injection (SSTI). Flask-Reuploaded has been patched…
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in version 1.5.0. Some workarounds are available. Do not pass user input to the `name` parameter, use auto-generated filenames only, and implement strict input validation if `name` must be used.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V1.3.2V1.3.7V1.3.10V5.3.2
Mitigating Controls (NIST 800-53 r5) AI
Enforces the intended directory access authorizations that path traversal would otherwise bypass.
Developer testing and static analysis can discover missing neutralization of template directives.
Input validation rejects or sanitizes untrusted data before it reaches the template engine, stopping injection of special syntax.
Least privilege reduces the impact of any unauthorized file access obtained via traversal.
Security engineering principles require use of safe templating APIs and proper escaping of external input.
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 input neutralization in template engines to prevent injection.
Patching/maintenance can remediate known path-traversal flaws in deployed software (partial prevention of exploitability) but does nothing to stop the coding defect from being introduced in the first place.
PR.AA-05 defines and reviews access policies but does not address code-level pathname neutralization, so neither direction prevents CWE-22.
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 can detect template-injection flaws but does not itself implement neutralization controls.
Secure development life cycle mandates input validation and sanitization that directly prevents template-injection weaknesses.
Application security requirements explicitly call for neutralizing special elements in template engines.
Secure architecture principles reduce the likelihood of unsafe template processing but do not prescribe specific neutralization techniques.
Secure coding standards require proper escaping or sandboxing of template directives, directly mitigating CWE-1336.
Information access restriction limits which files an application may read or write.