Habr•August 25, 2026•🇷🇺Translated from Russian

Starting in Bug Bounty: Understanding 1-Day Vulnerabilities

Mikhail Klyuchnikov, widely recognized in the bug hunting scene as n1, introduces readers to the fundamentals of 1-day vulnerabilities in the context of bug bounty programs.

Klyuchnikov has spent ten years at Positive Technologies, where he leads a group dedicated to software security analysis. His team focuses on two core activities: discovering previously unknown 0-day vulnerabilities and reproducing already disclosed 1-day vulnerabilities for use during penetration tests.

In addition to his work at Positive Technologies, Klyuchnikov participates in the PT SWARM team. Members of PT SWARM regularly publish technical articles, practical tips, and detailed breakdowns of vulnerabilities as soon as new information becomes available.

Over the years, Klyuchnikov has accumulated substantial experience participating in bug bounty programs on major international platforms as well as on the Russian platform Standoff Bug Bounty.

In this article, he sets out to explain what 1-day vulnerabilities are and how they fit into the workflow of researchers who are just beginning their journey in bug bounty hunting.

Related articles

Security NEXT•Vulnerabilities & Exploits

Apple Releases iOS 27.2 and iPadOS 27.2, Patching 163 Vulnerabilities Including Exploited Flaws in Older Versions

Apple has issued security updates for iOS and iPadOS, addressing a wide range of vulnerabilities across current and legacy operating systems. The iOS 27.2 and iPadOS 27.2 releases fix 163 CVEs affecting WebKit, the kernel, and image processing components. Older branches received targeted patches, with iOS 26.7.2 resolving 134 issues and iOS 18.7.11 addressing three vulnerabilities that include an actively exploited flaw. Specific fixes cover remote code execution risks in WebKit and ImageIO, plus sandbox bypasses. The updates were published on October 26, 2026, and apply to both iPhone and iPad devices. Apple also published detailed security content advisories for each branch.

Security NEXT•Vulnerabilities & Exploits

CISA Adds PHP2Shell Flaws CVE-2026-109618 and CVE-2026-109619 to KEV Catalog After Confirmed Exploitation

The U.S. Cybersecurity and Infrastructure Security Agency has confirmed active exploitation of two remotely exploitable vulnerabilities in PHP collectively known as PHP2Shell. CVE-2026-109618 stems from improper handling during memory exhaustion, while CVE-2026-109619 involves use-after-free issues in internal state management. Both flaws allow unauthenticated remote code execution and pose elevated risk to any PHP environment processing external requests such as web servers. PHP development teams released patches on October 21 for supported branches including PHP 8.5.12, 8.4.27, 8.3.36 and 8.2.35, along with source-level fixes for end-of-life versions 7.4, 8.0 and 8.1. CISA has set a three-day remediation deadline of October 29 for U.S. federal agencies and requires verification that systems have not been compromised.

Habr•Vulnerabilities & Exploits

Security Week 2644: Active Exploitation of PHP2Shell Vulnerabilities Confirmed

PHP developers released patches for two critical vulnerabilities collectively known as PHP2Shell on October 20, affecting PHP 8.2 through 8.5 as well as older branches. The flaws allow unauthenticated remote code execution on affected servers, which power approximately 70 percent of websites. Despite expectations of immediate exploitation, confirmed attacks with working exploits only began on October 25. CrowdStrike noted technical difficulties in weaponizing the issues in real-world environments. Only one-fifth of top Russian websites had applied the fixes by October 25. Additional incidents included compromised eMudhra certificates, a critical GitLab flaw, and a 16-year-old Broadcom router vulnerability.

AntiMalware•Vulnerabilities & Exploits

Positive Technologies Offers Up to 500,000 Rubles for Bypassing PT Application Firewall

Positive Technologies has expanded its Standoff Bug Bounty program to include rewards for bypassing its web application firewalls. Researchers can earn between 150,000 and 500,000 rubles for demonstrating practical bypasses against PT Application Firewall PRO and PT Application Firewall Cloud. The program targets the core protective mechanisms, including traffic filtering, attack detection rules, and the management layer used by administrators. Submissions must include reproducible attack scenarios that show how malicious requests can pass through undetected, rather than relying on scanner reports or theoretical findings. Reward amounts vary by severity and confirmed business impact, with critical issues in the PRO version paying up to 500,000 rubles. The company plans to use validated findings to strengthen detection rules and improve overall product resilience.