Seokchan Yoon

Seokchan Yoon

Offensive Web Security Researcher

Security Contributor of GitHub, Python, Django, FastAPI(Starlette), Apache Airflow, Ruby, Ruby-on-Rails, Java Spring

Education

March 2020 - February 2026

Bachelor's Degree in Computer Science & Engineering (Expected)

KyungHee University

July 2017 - May 2018

Completed Vulnerability Analysis Track

Best of the Best, Korean Next-Generation Security Leader Training Program

March 2017 - February 2020

Graduated from Dept. of Hacking Defense

Korea Digital Media Highschool

Work Experience

April 2025 - Present 11 months

Security Researcher

Zellic.io USA

  • Web2 systems and infrastructure security auditing
    • Conducted in-depth security reviews of complex Web2 environments, including SaaS platforms and virtual asset exchange infrastructure
    • Identified high-risk issues such as business logic flaws, denial-of-service, and SQL injection through white-box/gray-box testing
  • Security consulting and risk management
    • Worked directly with clients to propose and discuss optimal remediation plans that balance business continuity and security trade-offs
July 2025 - February 2026 8 months

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
March 2025 - February 2026 1 year

Undergraduate Researcher

PWNLAB (Kyung Hee University System Security Lab, Advisor: Daehee Jang)

  • 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)
September 2023 - March 2025 1 year 6 months

Unit [REDACTED], Private [REDACTED]

Research Institute under the Ministry of National Defense, Korea

  • Research and development of [REDACTED]
July 2020 - June 2023 3 years

R&D / Proactive Response Team, Security Engineer

STEALIEN

  • Web penetration testing
  • Development and operation of educational systems (Cyber Drill System, Django + React) and CTF
  • Development and maintenance of internal tools, technical blogs, deployment systems, and other infrastructure

CTF Awards

2025

CCE (Cyber Conflict Exercise)

Finalist

General Division

hosted by National Intelligence Service, Korea

Team: 경희대미남해커들 (KHU's hansome hackers)

2025

DEF CON CTF 33

Finalist

hosted by Nautilus Institute

Team: Cold Fusion

2024

🏆 White Hat Contest

1st

Soldier Division

hosted by Ministry of National Defense, Korea

Team: 키보드워리어플랫폼 (Keyboard Warrior Platform)

Korea Defense Minister Award

2023

CODEGATE

Finalist

University Division

hosted by Ministry of Science and ICT, Korea

Team: 경희대미남해커들 (KHU's hansome hackers)

2022

CODEGATE

Finalist

University Division

hosted by Ministry of Science and ICT, Korea

Team: 경희대미남해커들 (KHU's hansome hackers)

2022

🏆 CCE (Cyber Conflict Exercise)

2nd

Public Institution Sector Division

hosted by National Intelligence Service, Korea

Team: resilience

Korea Security Research Institute Director Award

2022

🏆 HACKTHEON SEJONG National University Cybersecurity Competition

6th

hosted by Sejong Special Self-Governing City, Korea

Team: 라임도둑 (Lime Thief)

Korea Security Research Institute Director Award

2021

🏆 CCE (Cyber Conflict Exercise)

2nd

Public Institution Sector Division

hosted by National Intelligence Service, Korea

Team: resilience

Korea Security Research Institute Director Award

2019

🏆 Cyber Operations Challenge

2nd

Student Division

hosted by Ministry of National Defense, Korea

Team: 윤석찬TV구독과좋아요알림설정까지

Korea Cyber Command Award

2018

🏆 Cybersecurity Competition

1st

Individual Preliminary Round

hosted by Ministry of Education, Korea

SWU President Award

2018

🏆 Cybersecurity Competition

1st

Team Finals

hosted by Ministry of Education, Korea

Team: 문시우1인팀 (munsiwoo 1-person team)

Education Minister Award

2017

🏆 Cybersecurity Competition

1st

Team Finals

hosted by Korea Education and Research Information Service

Team: 4-day exploit

KERIS Director Award

Disclosed Vulnerabilities

Django Django 10 Apache Airflow Apache Airflow 3 NAVER NAVER 3 Ruby on Rails Ruby on Rails 2 Python Python 1 FastAPI / Starlette FastAPI / Starlette 1 Ruby Ruby 1 Java Spring Java Spring 1 GitHub GitHub 1
Python

CVE-2024-7592

Denial of Service
7.5 High

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.

Django

CVE-2023-36053

Regular Expression Denial of Service
7.5 High

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.

Django

CVE-2024-24680

Denial of Service
7.5 High

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.

Django

CVE-2024-27351

Regular Expression Denial of Service
5.3 Medium

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.

Django

CVE-2024-21520

Cross-Site Scripting
6.1 Medium

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.

Django

CVE-2024-41991

Denial of Service
7.5 High

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.

Django

CVE-2024-53908

SQL Injection
9.8 Critical

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.)

Django

CVE-2025-48432

Log Injection
5.3 Medium

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.

Django

CVE-2025-64458

Denial of Service
7.5 High

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.

Django

CVE-2025-64460

Denial of Service
7.5 High

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.

Django

CVE-2026-1285

Denial of Service
7.5 High

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.

FastAPI / Starlette

CVE-2025-62727

Denial of Service
7.5 High

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).

Apache Airflow

CVE-2024-39877

Code Execution
8.8 High

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.

Apache Airflow

CVE-2024-39863

Cross-Site Scripting
5.4 Medium

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.

Apache Airflow

CVE-2024-45034

Code Execution
8.8 High

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.

Ruby

CVE-2024-41123

Denial of Service
7.5 High

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 ]>.

Ruby on Rails

CVE-2024-47887

Regular Expression Denial of Service
6.0 Medium

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.

Ruby on Rails

CVE-2024-41128

Regular Expression Denial of Service
6.0 Medium

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.

Java Spring

CVE-2024-38809

Denial of Service
5.3 Medium

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.

GitHub

HackerOne #2646500

Denial of Service

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.

NAVER

NBB-1126

Stored XSS

Stored XSS

NAVER is vulnerable to a stored-xss caused by a crafted payload.

NAVER

NBB-1143

SQL Injection

SQL Injection

NAVER is vulnerable to a SQL injection caused by a crafted payload.

NAVER

NBB-1260

Stored XSS

Stored XSS

NAVER is vulnerable to a stored XSS caused by a crafted payload.

Talks

“Django Framework from a Hacker's Perspective” (in Korean)

PyCon KR 2024

2024

“Analysis of Django Framework N-day Vulnerabilities and Secure Coding Guide” (in Korean)

CODEGATE 2023

2023

“Django Framework 1-day Analysis” (in Korean)

26th Hacking Camp

2023

“Bug Cases and Secure Coding in Modern Web Services” (in Korean)

STEALIEN Security Seminar

2022

Blog Posts