{"id":36029,"date":"2026-01-16T09:32:01","date_gmt":"2026-01-16T09:32:01","guid":{"rendered":"http:\/\/localhost\/?p=36029"},"modified":"2026-01-16T09:32:01","modified_gmt":"2026-01-16T09:32:01","slug":"nu-html-checker-validatornu-restriction-bypass-vulnerability-allowing-local-ssrf","status":"publish","type":"post","link":"https:\/\/zero.redgem.net\/?p=36029","title":{"rendered":"Nu Html Checker (validator.nu) &#8211; Restriction bypass vulnerability allowing local SSRF_CVE-2025-15104"},"content":{"rendered":"<p>{&#8220;lastseen&#8221;:&#8221;&#8221;,&#8221;description&#8221;:&#8221;Nu Html Checker (validator.nu) contains a restriction bypass that allows remote attackers to make the server perform arbitrary HTTP\/HTTPS requests to internal resources, including localhost services. While the validator implements hostname-based protections to block direct access to localhost and 127.0.0.1, these controls can be bypassed using DNS rebinding techniques or domains that resolve to loopback addresses.This issue affects The Nu Html Checker (vnu): latest (commit 23f090a11bab8d0d4e698f1ffc197a4fe226a9cd).&#8221;,&#8221;published&#8221;:&#8221;2026-01-16T14:00:16.643Z&#8221;,&#8221;modified&#8221;:&#8221;2026-01-16T14:30:55.715Z&#8221;,&#8221;type&#8221;:&#8221;cve&#8221;,&#8221;title&#8221;:&#8221;Nu Html Checker (validator.nu) &#8211; Restriction bypass vulnerability allowing local SSRF&#8221;,&#8221;source&#8221;:&#8221;Fluid Attacks&#8221;,&#8221;references&#8221;:&#8221;https:\/\/fluidattacks.com\/advisories\/europe\\nhttps:\/\/github.com\/validator\/validator&#8221;,&#8221;id&#8221;:&#8221;CVE-2025-15104&#8243;,&#8221;bulletinFamily&#8221;:&#8221;&#8221;,&#8221;cwe&#8221;:[&#8220;CWE-918&#8243;],&#8221;cvelist&#8221;:null,&#8221;sourceData&#8221;:&#8221;The Nu Html Checker The Nu Html Checker latest &#8211; 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commit:23f090a11bab8d0d4e698f1ffc197a4fe226a9cd&#8221;,&#8221;vendor&#8221;:&#8221;The Nu Html Checker&#8221;,&#8221;ai_description&#8221;:&#8221;&#8221;,&#8221;ai_severity&#8221;:&#8221;&#8221;,&#8221;ai_vendor&#8221;:&#8221;&#8221;,&#8221;ai_product&#8221;:&#8221;&#8221;,&#8221;ai_version&#8221;:&#8221;&#8221;,&#8221;ai_score&#8221;:0}<\/p>\n","protected":false},"excerpt":{"rendered":"<p>{&#8220;lastseen&#8221;:&#8221;&#8221;,&#8221;description&#8221;:&#8221;Nu Html Checker (validator.nu) contains a restriction bypass that allows remote attackers to make the server perform arbitrary HTTP\/HTTPS requests to internal resources, including localhost&#8230;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[6,8,48,12,21,13,7,11,5],"class_list":["post-36029","post","type-post","status-publish","format-standard","hentry","category-category_cve","tag-cve","tag-cvss","tag-cvss-69","tag-exploit","tag-medium","tag-news","tag-security","tag-tapic","tag-vulnerability"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.5 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Nu Html Checker (validator.nu) - Restriction bypass vulnerability allowing local SSRF_CVE-2025-15104 - zero redgem<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/zero.redgem.net\/?p=36029\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Nu Html Checker (validator.nu) - Restriction bypass vulnerability allowing local SSRF_CVE-2025-15104 - zero redgem\" \/>\n<meta property=\"og:description\" content=\"{&#8220;lastseen&#8221;:&#8221;&#8221;,&#8221;description&#8221;:&#8221;Nu Html Checker (validator.nu) contains a restriction bypass that allows remote attackers to make the server perform arbitrary HTTP\/HTTPS requests to internal resources, including localhost...\" \/>\n<meta property=\"og:url\" content=\"https:\/\/zero.redgem.net\/?p=36029\" \/>\n<meta property=\"og:site_name\" content=\"zero redgem\" \/>\n<meta property=\"article:published_time\" content=\"2026-01-16T09:32:01+00:00\" \/>\n<meta name=\"author\" content=\"invoker\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"invoker\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"1 minute\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\\\/\\\/zero.redgem.net\\\/?p=36029#article\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/zero.redgem.net\\\/?p=36029\"},\"author\":{\"name\":\"invoker\",\"@id\":\"https:\\\/\\\/zero.redgem.net\\\/#\\\/schema\\\/person\\\/fbfeae8dfad117ac08a7621bee1a1dca\"},\"headline\":\"Nu Html Checker (validator.nu) &#8211; 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