Seokchan Yoon
Offensive Web Security Researcher
Security Contributor of GitHub, GitLab, Python, Django, FastAPI(Starlette), Apache Airflow, Ruby, Ruby-on-Rails, Shopify, Java Spring
- DEF CON 33 CTF Finalist. Active CTF competitor since 2016 (10 years)
- Awarded Defense Minister Award (2024), National Security Research Institute Director Award (2022, 2021), Cyber Operations Command Award (2019), Education Minister Award (2018)
- Listed in Google and Naver Bug Bounty Hall of Fame
Education
Graduated from Computer Science & Engineering
KyungHee University
Completed Vulnerability Analysis Track
Best of the Best, Korean Next-Generation Security Leader Training Program
Graduated from Dept. of Hacking Defense
Korea Digital Media Highschool
Work Experience
Security Researcher
Zellic.io USA
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Web2 System Security Auditing
- Conducted source code-based security audits targeting Web2 infrastructure of global blockchain projects
- Identified architectural flaws difficult to detect through external testing alone via white-box/gray-box analysis of internal structures
- Performed pair audits across diverse tech stacks (Node.js, Go, Python, Rust) spanning DeFi, exchanges, and social platforms, discovering numerous high-risk vulnerabilities including authentication bypass, business logic flaws, and DoS
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Audit Reporting and Global Client Engagement
- Assessed risk levels and business impact of discovered vulnerabilities and authored English-language audit reports
- Communicated directly with US-based clients in English, managing the full cycle from audit reporting to patch re-verification
- Collaborated with the smart contract audit team to comprehensively evaluate compound risks at the Web2/Web3 boundary
Security Team Member (Volunteer)
Airflow Security Team, Apache Software Foundation USA
- Reviewing and addressing security vulnerabilities in Apache Airflow
- Collaborating with the open-source community
- Maintaining the security posture of the project in accordance with ASF guidelines
Undergraduate Researcher
PWNLAB (Kyung Hee University System Security Lab, Advisor: Daehee Jang)
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Samsung multi-cloud integrated security verification tool development and web service penetration testing
- Implemented an IaC-based scanner that automatically diagnoses ~260 security compliance items across AWS, GCP, and Azure (IAM, Network, Container, Database, Storage, Monitoring, Logging, etc.) (Python, FastAPI)
- Designed an agentless architecture and multi-threaded parallel scan engine optimized for large-scale enterprise environments
- Performed black-box penetration testing for 19 Samsung-owned web services and identified 10 major vulnerabilities -- IDOR, file upload filter bypass, XSS, and other medium-impact issues with remediation guidance
- Maintained and developed features for the system hacking wargame `pwnable.kr` (PHP)
Unit [REDACTED], Private [REDACTED]
Research Institute under the Ministry of National Defense, Korea
- Research and development of [REDACTED]
R&D / Proactive Response Team, Security Engineer
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Web Penetration Testing / Red Teaming
- Conducted numerous penetration tests over 3 years targeting web services across major industries including finance, enterprises, and government agencies
- Performed black-box assessments on diverse environments such as KB Kookmin Bank, Hana Bank, Ministry of Culture, Sports and Tourism and Ministry of Foreign Affairs-affiliated services, and Lotte Castle IoT systems
- Executed a penetration testing engagement for the City of Bandung, Indonesia web services
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CTF Platform Development and Operation
- Designed and developed a custom web-based CTF platform (Django + React)
- Managed the full pipeline of distributing, collecting, and uploading challenges across ~20 problem setters
- Operated on-site competitions including the Ministry of Education Cybersecurity Competition and Ko-World CTF at Dubai GITEX
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Internal Security Infrastructure
- Designed and built internal GitLab, tech blog, deployment systems, and internal network environment to prevent external leakage of exploits
CTF Awards
CCE (Cyber Conflict Exercise)
General Division
hosted by National Intelligence Service, Korea
Team: 경희대미남해커들 (KHU's hansome hackers)
DEF CON CTF 33
hosted by Nautilus Institute
Team: Cold Fusion
🏆 White Hat Contest
Soldier Division
hosted by Ministry of National Defense, Korea
Team: 키보드워리어플랫폼 (Keyboard Warrior Platform)
Korea Defense Minister Award
CODEGATE
University Division
hosted by Ministry of Science and ICT, Korea
Team: 경희대미남해커들 (KHU's hansome hackers)
CODEGATE
University Division
hosted by Ministry of Science and ICT, Korea
Team: 경희대미남해커들 (KHU's hansome hackers)
🏆 CCE (Cyber Conflict Exercise)
Public Institution Sector Division
hosted by National Intelligence Service, Korea
Team: resilience
Korea Security Research Institute Director Award
🏆 HACKTHEON SEJONG National University Cybersecurity Competition
hosted by Sejong Special Self-Governing City, Korea
Team: 라임도둑 (Lime Thief)
Korea Security Research Institute Director Award
🏆 CCE (Cyber Conflict Exercise)
Public Institution Sector Division
hosted by National Intelligence Service, Korea
Team: resilience
Korea Security Research Institute Director Award
🏆 Cyber Operations Challenge
Student Division
hosted by Ministry of National Defense, Korea
Team: 윤석찬TV구독과좋아요알림설정까지
Korea Cyber Command Award
🏆 Cybersecurity Competition
Individual Preliminary Round
hosted by Ministry of Education, Korea
SWU President Award
🏆 Cybersecurity Competition
Team Finals
hosted by Ministry of Education, Korea
Team: 문시우1인팀 (munsiwoo 1-person team)
Education Minister Award
🏆 Cybersecurity Competition
Team Finals
hosted by Korea Education and Research Information Service
Team: 4-day exploit
KERIS Director Award
Disclosed Vulnerabilities
CVE 21
CVE-2024-7592: Quadratic complexity parsing cookies with backslashes
There is a LOW severity vulnerability affecting CPython, specifically the 'http.cookies' standard library module. When parsing cookies that contained backslashes for quoted characters in the cookie value, the parser would use an algorithm with quadratic complexity, resulting in excess CPU resources being used while parsing the value.
CVE-2023-36053: Potential regular expression denial of service vulnerability in EmailValidator/URLValidator
In Django 3.2 before 3.2.20, 4 before 4.1.10, and 4.2 before 4.2.3, EmailValidator and URLValidator are subject to a potential ReDoS (regular expression denial of service) attack via a very large number of domain name labels of emails and URLs.
CVE-2024-24680: Potential denial-of-service in intcomma template filter
An issue was discovered in Django 3.2 before 3.2.24, 4.2 before 4.2.10, and Django 5.0 before 5.0.2. The intcomma template filter was subject to a potential denial-of-service attack when used with very long strings.
CVE-2024-27351: Potential regular expression denial-of-service in django.utils.text.Truncator.words()
In Django 3.2 before 3.2.25, 4.2 before 4.2.11, and 5.0 before 5.0.3, the django.utils.text.Truncator.words() method (with html=True) and the truncatewords_html template filter are subject to a potential regular expression denial-of-service attack via a crafted string. NOTE: this issue exists because of an incomplete fix for CVE-2019-14232 and CVE-2023-43665.
CVE-2024-21520: Cross-Site Scripting (XSS) in browserable API of django-rest-framework
Versions of the package djangorestframework before 3.15.2 are vulnerable to Cross-site Scripting (XSS) via the break_long_headers template filter due to improper input sanitization before splitting and joining with <br> tags.
CVE-2024-41991: Potential denial-of-service vulnerability in django.utils.html.urlize() and AdminURLFieldWidget
An issue was discovered in Django 5.0 before 5.0.8 and 4.2 before 4.2.15. The urlize and urlizetrunc template filters, and the AdminURLFieldWidget widget, are subject to a potential denial-of-service attack via certain inputs with a very large number of Unicode characters.
CVE-2024-53908: Potential SQL injection in HasKey(lhs, rhs) on Oracle
An issue was discovered in Django 5.1 before 5.1.4, 5.0 before 5.0.10, and 4.2 before 4.2.17. Direct usage of the django.db.models.fields.json.HasKey lookup, when an Oracle database is used, is subject to SQL injection if untrusted data is used as an lhs value. (Applications that use the jsonfield.has_key lookup via __ are unaffected.)
CVE-2025-48432: Potential log injection via unescaped request path
An issue was discovered in Django 5.2 before 5.2.3, 5.1 before 5.1.11, and 4.2 before 4.2.23. Internal HTTP response logging does not escape request.path, which allows remote attackers to potentially manipulate log output via crafted URLs. This may lead to log injection or forgery when logs are viewed in terminals or processed by external systems.
CVE-2025-64458: Potential denial-of-service vulnerability in HttpResponseRedirect and HttpResponsePermanentRedirect on Windows
NFKC normalization in Python is slow on Windows. As a consequence, django.http.HttpResponseRedirect, django.http.HttpResponsePermanentRedirect, and the shortcut django.shortcuts.redirect were subject to a potential denial-of-service attack via certain inputs with a very large number of Unicode characters.
CVE-2025-64460: Potential denial-of-service vulnerability in XML serializer text extraction
Algorithmic complexity in django.core.serializers.xml_serializer.getInnerText() allows a remote attacker to cause a potential denial-of-service attack triggering CPU and memory exhaustion via specially crafted XML input processed by the XML Deserializer.
CVE-2026-1285: Potential denial-of-service vulnerability in django.utils.text.Truncator HTML methods
django.utils.text.Truncator.chars() and Truncator.words() methods (with html=True) and the truncatechars_html and truncatewords_html template filters allow a remote attacker to cause a potential denial-of-service via crafted inputs containing a large number of unmatched HTML end tags.
CVE-2026-25673: Potential denial-of-service vulnerability in URLField via Unicode normalization on Windows
On Windows, urllib.parse.urlsplit() performs NFKC normalization (unicodedata.normalize), which can be disproportionately slow for large inputs containing certain characters. django.forms.URLField.to_python() used urlsplit() for scheme detection, making it vulnerable to denial-of-service via specially crafted POST payloads.
CVE-2025-62727: Starlette vulnerable to O(n^2) DoS via Range header merging
An unauthenticated attacker can send a crafted HTTP Range header that triggers quadratic-time processing in Starlette's FileResponse Range parsing/merging logic. This enables CPU exhaustion per request, causing denial-of-service for endpoints serving files (e.g., StaticFiles or any use of FileResponse).
CVE-2024-39877: Apache Airflow: DAG Author Code Execution possibility in airflow-scheduler
Apache Airflow 2.4.0, and versions before 2.9.3, has a vulnerability that allows authenticated DAG authors to craft a doc_md parameter in a way that could execute arbitrary code in the scheduler context, which should be forbidden according to the Airflow Security model.
CVE-2024-39863: Apache Airflow: Potential XSS Vulnerability
Apache Airflow versions before 2.9.3 have a vulnerability that allows an authenticated attacker to inject a malicious link when installing a provider.
CVE-2024-45034: Apache Airflow: Authenticated DAG authors could execute code on scheduler nodes
Apache Airflow versions before 2.10.1 have a vulnerability that allows DAG authors to add local settings to the DAG folder and get it executed by the scheduler, where the scheduler is not supposed to execute code submitted by the DAG author.
CVE-2024-56373: Apache Airflow: Code Injection via Log Template History
Apache Airflow before 2.11.1 has a vulnerability that allows a DAG author to manipulate the database to execute arbitrary code in the web-server context via the log template history feature, leading to potential remote code execution when a user views historical task information.
CVE-2024-41123: DoS vulnerabilities in REXML
The REXML gem before 3.3.2 has some DoS vulnerabilities when it parses an XML that has many specific characters such as whitespace character, >] and ]>.
CVE-2024-47887: Possible ReDoS vulnerability in HTTP Token authentication in Action Controller
There is a possible ReDoS vulnerability in Action Controller's HTTP Token authentication. For applications using HTTP Token authentication via authenticate_or_request_with_http_token or similar, a carefully crafted header may cause header parsing to take an unexpected amount of time, possibly resulting in a DoS vulnerability.
CVE-2024-41128: Possible ReDoS vulnerability in query parameter filtering in Action Dispatch
There is a possible ReDoS vulnerability in the query parameter filtering routines of Action Dispatch. Carefully crafted query parameters can cause query parameter filtering to take an unexpected amount of time, possibly resulting in a DoS vulnerability.
CVE-2024-38809: Spring Framework DoS via conditional HTTP request
Applications that parse ETags from "If-Match" or "If-None-Match" request headers are vulnerable to DoS attack.
Bug Bounty & Others 8
HackerOne #3550632: SSRF via [REDACTED] on gitlab.com allows [REDACTED] exfiltration
GitLab is vulnerable to a server-side request forgery via [REDACTED], allowing an attacker to exfiltrate [REDACTED].
HackerOne #3551313: Open Redirect in [REDACTED] via [REDACTED] parameter
Shopify is vulnerable to an open redirect in [REDACTED] due to an unvalidated [REDACTED] parameter, allowing an attacker to redirect users to [REDACTED].
HackerOne #2646500: DoS Vulnerability in GitHub Enterprise
GitHub and GitHub Enterprise are vulnerable to a potential denial-of-service attack caused by a maliciously crafted HTTP request.
NBB-1126: Stored XSS
NAVER is vulnerable to a stored-xss caused by a crafted payload.
NBB-1143: SQL Injection
NAVER is vulnerable to a SQL injection caused by a crafted payload.
NBB-1260: Stored XSS
NAVER is vulnerable to a stored XSS caused by a crafted payload.
NBB-2026-0028: Reflected XSS on NAVER OO Service
NAVER is vulnerable to a reflected XSS caused by a crafted payload.
NBB-2026-0029: Reflected XSS on NAVER OO Service
NAVER is vulnerable to a reflected XSS caused by a crafted payload.
Talks
“Django Framework from a Hacker's Perspective” (in Korean)
PyCon KR 2024
“Analysis of Django Framework N-day Vulnerabilities and Secure Coding Guide” (in Korean)
CODEGATE 2023
“Django Framework 1-day Analysis” (in Korean)
26th Hacking Camp
“Bug Cases and Secure Coding in Modern Web Services” (in Korean)
STEALIEN Security Seminar
Blog Posts
How I Found a $2,163 Vulnerability with a $5 Prompt
https://new-blog.ch4n3.kr/llm-found-security-issues-from-django-en/
DEF CON 33 CTF Review
https://new-blog.ch4n3.kr/def-con-33-review-en/
Is Airflow Truly Safe? ー With Reviews of Disclosed Vulnerabilities
https://new-blog.ch4n3.kr/is-airflow-truly-safe-en/
Your Django App Is Vulnerable to DoS Attacks: Update Your Python Version Now
https://new-blog.ch4n3.kr/cve-2024-7592-en/
Review for Recent Django Security Issues - CVE-2024-24680, CVE-2024-27351
https://new-blog.ch4n3.kr/reviews-for-2024-django-security-issues/
Do not use `maildev` anyway 💣
https://new-blog.ch4n3.kr/do-not-use-maildev-anyway/