Daniel Kaminsky (February 7, 1979 – April 23, 2021) was an American computer security researcher. He was a co-founder and chief scientist of Human Security (formerly White Ops), a computer security company. He previously worked for Cisco, Avaya, and IOActive, where he was the director of penetration testing. The New York Times labeled Kaminsky an "Internet security savior" and "a digital Paul Revere".

Kaminsky was known among computer security experts for his work on DNS cache poisoning, for showing that the Sony rootkit had infected at least 568,000 computers, and for his talks at the Black Hat Briefings. On June 16, 2010, he was named by ICANN as one of the Trusted Community Representatives for the DNSSEC root.

Daniel Kaminsky was born in San Francisco on February 7, 1979, to Marshall Kaminsky and Trudy Maurer. His mother told The New York Times that after his father bought him a RadioShack computer at age four, Kaminsky had taught himself to code by age five. At 11, his mother received a call from a government security administrator who told her that Kaminsky had used penetration testing to intrude into military computers, and that the family's Internet would be cut off. His mother responded by saying if their access was cut, she would take out an advertisement in the San Francisco Chronicle to publicize the fact that an 11-year-old could break military computer security. Instead, a three-day Internet "timeout" for Kaminsky was negotiated. In 2008, after Kaminsky found and coordinated a fix for a fundamental DNS flaw, he was approached by the administrator, who thanked him and asked to be introduced to his mother.

Kaminsky attended St. Ignatius College Preparatory and Santa Clara University. After graduating from college, he worked for Cisco, Avaya, and IOActive, before founding his own firm White Ops (later renamed Human Security).

During the Sony BMG copy protection rootkit scandal, where Sony BMG was found to be covertly installing anti-piracy software onto PCs, Kaminsky used DNS cache snooping to discover whether servers had recently contacted any of the domains accessed by the Sony rootkit. He used this technique to estimate that there were at least 568,000 networks that had computers with the rootkit. Kaminsky then used his research to bring more awareness to the issue while Sony executives were trying to play it down.

In April 2008, Kaminsky realized a growing practice among ISPs potentially represented a security vulnerability. Various ISPs have experimented with intercepting return messages of non-existent domain names and replacing them with advertising content. This could allow hackers to set up phishing schemes by attacking the server responsible for the advertisements and linking to non-existent subdomains of the targeted websites. Kaminsky demonstrated this process by setting up Rickrolls on Facebook and PayPal. While the vulnerability used initially depended in part on the fact that Earthlink was using Barefruit to provide its advertising, Kaminsky was able to generalize the vulnerability to attack Verizon by attacking its ad provider, Paxfire.

Kaminsky went public after working with the ad networks in question to eliminate the immediate cross-site scripting vulnerability.

In 2008, Kaminsky discovered a fundamental flaw in the Domain Name System (DNS) protocol that could allow attackers to easily perform cache poisoning attacks on most nameservers (djbdns, PowerDNS, MaraDNS, Secure64 and Unbound were not vulnerable). With most Internet-based applications depending on DNS to locate their peers, a wide range of attacks became feasible, including website impersonation, email interception, and authentication bypass via the "Forgot My Password" feature on many popular websites. After discovering the problem, Kaminsky initially contacted Paul Vixie, who described the severity of the issue as meaning "everything in the digital universe was going to have to get patched." Kaminsky then alerted the Department of Homeland Security and executives at Cisco and Microsoft to work on a fix.