{"id":14062,"date":"2026-10-04T20:20:46","date_gmt":"2026-10-04T20:20:46","guid":{"rendered":"https:\/\/cryptonews.uk.com\/?p=14062"},"modified":"2026-10-04T20:20:46","modified_gmt":"2026-10-04T20:20:46","slug":"bitcoin-cores-new-fix-closes-gap-that-could-redirect-funds-without-stealing-keys","status":"publish","type":"post","link":"https:\/\/cryptonews.uk.com\/?p=14062","title":{"rendered":"Bitcoin Core\u2019s new fix closes gap that could redirect funds without stealing keys"},"content":{"rendered":"<p><\/p>\n<div data-cs-editorial-figure-scope=\"\" data-cs-editorial-quote-scope=\"\" data-cs-image-viewer-scope=\"\" data-single-article-content=\"\">\n<p>Bitcoin Core has added a safeguard against signing transactions that may not bind funds to the payment destination a user approved.<\/p>\n<p>The change, merged into Bitcoin Core\u2019s master development branch on Sept. 25, targets a narrow flaw in partially signed Bitcoin transactions, or PSBTs, that could produce a valid signature without protecting the intended output.<\/p>\n<p>Bitcoin Optech highlighted the update on Oct. 2. The issue does not expose a user\u2019s private key, but creates a different risk: a signature can remain valid even when the transaction\u2019s recipient is changed under specific conditions.<\/p>\n<p>The weakness involves <code>SIGHASH_SINGLE<\/code>which is a signing mode designed to commit an input to the output in the corresponding position. If the transaction contains no output at that position, the protection breaks down differently depending on the type of Bitcoin being spent.<\/p>\n<p><img loading=\"lazy\" loading=\"lazy\" decoding=\"async\" class=\"aligncenter shoggoth-infographic shoggoth-infographic-portrait wp-image-568832\" src=\"https:\/\/cryptoslate.com\/wp-content\/uploads\/2026\/10\/exec-cc9446b2-76db-4916-9113-bf9721e1e212.png\" alt=\"SIGHASH_SINGLE diagram with two inputs and one output: the second input lacks a matching output. Legacy signs a fixed hash and may allow reuse for other same-key coins; SegWit v0 retains input commitments but leaves outputs unbound. Core skips the affected input while signing other eligible inputs.\" width=\"720\" height=\"900\" srcset=\"https:\/\/cryptoslate.com\/wp-content\/uploads\/2026\/10\/exec-cc9446b2-76db-4916-9113-bf9721e1e212.png 1122w, https:\/\/cryptoslate.com\/wp-content\/uploads\/2026\/10\/exec-cc9446b2-76db-4916-9113-bf9721e1e212-240x300.png 240w, https:\/\/cryptoslate.com\/wp-content\/uploads\/2026\/10\/exec-cc9446b2-76db-4916-9113-bf9721e1e212-819x1024.png 819w, https:\/\/cryptoslate.com\/wp-content\/uploads\/2026\/10\/exec-cc9446b2-76db-4916-9113-bf9721e1e212-768x960.png 768w\" sizes=\"auto, (max-width: 720px) 100vw, 720px\"\/><img loading=\"lazy\" loading=\"lazy\" decoding=\"async\" class=\"lazyload aligncenter shoggoth-infographic shoggoth-infographic-portrait wp-image-568832\" src=\"https:\/\/cryptoslate.com\/wp-content\/uploads\/2026\/10\/exec-cc9446b2-76db-4916-9113-bf9721e1e212.png\" alt=\"SIGHASH_SINGLE diagram with two inputs and one output: the second input lacks a matching output. Legacy signs a fixed hash and may allow reuse for other same-key coins; SegWit v0 retains input commitments but leaves outputs unbound. Core skips the affected input while signing other eligible inputs.\" width=\"720\" height=\"900\" srcset=\"https:\/\/cryptoslate.com\/wp-content\/uploads\/2026\/10\/exec-cc9446b2-76db-4916-9113-bf9721e1e212.png 1122w, https:\/\/cryptoslate.com\/wp-content\/uploads\/2026\/10\/exec-cc9446b2-76db-4916-9113-bf9721e1e212-240x300.png 240w, https:\/\/cryptoslate.com\/wp-content\/uploads\/2026\/10\/exec-cc9446b2-76db-4916-9113-bf9721e1e212-819x1024.png 819w, https:\/\/cryptoslate.com\/wp-content\/uploads\/2026\/10\/exec-cc9446b2-76db-4916-9113-bf9721e1e212-768x960.png 768w\" data-sizes=\"(max-width: 720px) 100vw, 720px\"\/><\/p>\n<p>For legacy inputs, the missing-output case can produce a signature over a fixed hash value. Bitcoin Core developers said that signature may then be reusable against other unspent outputs controlled by the same key when the same structural conditions are present.<\/p>\n<p>SegWit v0 transactions retain stronger protections because the signature still commits to the specific coin being spent and its amount. The destination output, however, can remain unbound.<\/p>\n<aside id=\"cs-inline-newsletter-1\" class=\"cs-inline-newsletter\" data-inline-newsletter=\"\" data-newsletter-placement=\"article-midpoint\" data-newsletter-pending-label=\"Joining\u2026\" data-newsletter-pending-status=\"Joining The Catalyst\u2026\" data-newsletter-email-required-message=\"Before sending, please provide your email address.\" aria-labelledby=\"cs-inline-newsletter-1-title\" aria-describedby=\"cs-inline-newsletter-1-copy\">\n<div class=\"cs-inline-newsletter__inner\">\n<div class=\"cs-inline-newsletter__content\"> <span class=\"cs-inline-newsletter__eyebrow\"> <i class=\"fa-regular fa-envelope\" aria-hidden=\"true\"\/> The Catalyst <\/span><\/p>\n<h2 id=\"cs-inline-newsletter-1-title\" class=\"cs-inline-newsletter__title\">What\u2019s moving crypto. Why it matters.<\/h2>\n<p id=\"cs-inline-newsletter-1-copy\" class=\"cs-inline-newsletter__copy\">Get CryptoSlate\u2019s essential stories and what to watch next.<\/p>\n<p>  <svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"16\" height=\"16\" fill=\"currentColor\" viewbox=\"0 0 16 16\" aria-hidden=\"true\" focusable=\"false\"> <path d=\"M15 3.604H1v1.891h14v-1.89ZM1 7.208V16l7-3.926L15 16V7.208zM15 0H1v1.89h14z\"\/> <\/svg> <span>Published on Substack<\/span> <\/div>\n<div class=\"cs-inline-newsletter__form-shell\">\n<p id=\"cs-inline-newsletter-1-privacy\" class=\"cs-inline-newsletter__privacy\">Seven days a week. Unsubscribe anytime.<\/p>\n<p> <i class=\"fa-regular fa-circle-xmark\" aria-hidden=\"true\"\/> <span>Whoops, looks like there was a problem. Please try again.<\/span><\/p>\n<div class=\"cs-inline-newsletter__success\" role=\"status\" aria-live=\"polite\" aria-atomic=\"true\" tabindex=\"-1\"> <span class=\"cs-inline-newsletter__success-icon\" aria-hidden=\"true\"\/><\/p>\n<div>\n<h3 class=\"cs-inline-newsletter__success-title\">Check your inbox.<\/h3>\n<p class=\"cs-inline-newsletter__success-copy\">Your signup request was sent. If confirmation is required, follow the email from Substack.<\/p>\n<p class=\"cs-inline-newsletter__success-hint\">Look in spam or promotions if you don\u2019t see it.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/aside>\n<p>That creates an authorization problem for wallets and signing devices: software could present one payment to the user while producing a signature that does not cryptographically guarantee that the approved recipient remains unchanged.<\/p>\n<h2>Bitcoin Core blocks the risky signing request<\/h2>\n<p>Bitcoin Core already rejected the edge case through its raw-transaction signing interface. Its PSBT path, including <code>walletprocesspsbt<\/code>could still sign it.<\/p>\n<p>The new code moves the check into Bitcoin Core\u2019s shared signature-creation logic, preventing affected legacy and SegWit v0 inputs from being signed while allowing other valid inputs in the same PSBT to proceed.<\/p>\n<p>PSBTs are commonly used to coordinate transactions between software wallets, hardware devices and offline signers. They allow transaction builders to pass information to a separate signer without giving that system control of the private keys.<\/p>\n<p>The fix therefore reinforces a boundary that wallet developers must enforce independently of key security: a valid cryptographic signature must commit to the transaction details the user actually authorized.<\/p>\n<p>Bitcoin Improvement Proposal 174, which defines PSBTs, already tells signers to reject unacceptable signing modes and recommends <code>SIGHASH_ALL<\/code> when no alternative is specified. The Bitcoin Core change explicitly prevents this missing-output configuration from reaching the signing stage.<\/p>\n<div class=\"cs-article-embed\">\n<p> <span class=\"cs-article-embed__related-reading\">Related Reading<\/span><\/p>\n<h3 class=\"cs-article-embed__title\">Major Bitcoin Core update changes default wallet protocols, risking temporary disruption across popular apps<\/h3>\n<\/p>\n<p> <span class=\"cs-article-embed__arrow\" aria-hidden=\"true\"> <i class=\"fa-light fa-arrow-up-right\"\/> <\/span> <\/div>\n<p>Users do not yet have a confirmed production release containing the safeguard. The Sept. 25 change was merged into Bitcoin Core\u2019s development branch, while the project\u2019s published release listings had not identified a fixed version or confirmed backport as of Oct. 4.<\/p>\n<p>That leaves wallet providers and hardware-signing integrations with the more immediate decision: review their own handling of <code>SIGHASH_SINGLE<\/code> requests rather than waiting for a Bitcoin Core release to enforce the same protection downstream.<\/p>\n<\/div>\n<p>Featured,Payments,Technology,Wallets,Bitcoin,BTC,paymentsBitcoin,BTC,payments#Bitcoin #Cores #fix #closes #gap #redirect #funds #stealing #keys1791145246<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Bitcoin Core has added a safeguard against signing transactions that may not bind funds to the payment destination a user approved. The change, merged into Bitcoin Core\u2019s master development branch on Sept. 25, targets a narrow flaw in partially signed Bitcoin transactions, or PSBTs, that could produce a valid signature without protecting the intended output.<\/p>\n","protected":false},"author":1,"featured_media":14063,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8],"tags":[91,285,191,7258,1053,1238,737,354,167,7259,1942],"class_list":["post-14062","post","type-post","status-publish","format-standard","has-post-thumbnail","category-ethereum","tag-bitcoin","tag-btc","tag-closes","tag-cores","tag-fix","tag-funds","tag-gap","tag-keys","tag-payments","tag-redirect","tag-stealing"],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v26.6 (Yoast SEO v26.6) - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Bitcoin Core\u2019s new fix closes gap that could redirect funds without stealing keys - Crypto News: Latest Cryptocurrency News and Analysis<\/title>\n<meta name=\"description\" content=\"Bitcoin Core will now refuse certain malformed PSBT signing requests where the matching transaction output is missing.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/cryptonews.uk.com\/?p=14062\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Bitcoin Core\u2019s new fix closes gap that could redirect funds without stealing keys\" \/>\n<meta property=\"og:description\" content=\"Bitcoin Core will now refuse certain malformed PSBT signing requests where the matching transaction output is missing.\" \/>\n<meta property=\"og:url\" content=\"https:\/\/cryptonews.uk.com\/?p=14062\" \/>\n<meta property=\"og:site_name\" content=\"Crypto News: Latest Cryptocurrency News and Analysis\" \/>\n<meta property=\"article:published_time\" content=\"2026-10-04T20:20:46+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/cryptonews.uk.com\/wp-content\/uploads\/2026\/10\/psbt-output-check-v2.webp\" \/>\n\t<meta property=\"og:image:width\" content=\"1280\" \/>\n\t<meta property=\"og:image:height\" content=\"720\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/webp\" \/>\n<meta name=\"author\" content=\"\u884c\u653f\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"\u884c\u653f\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"3 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"WebPage\",\"@id\":\"https:\/\/cryptonews.uk.com\/?p=14062\",\"url\":\"https:\/\/cryptonews.uk.com\/?p=14062\",\"name\":\"Bitcoin Core\u2019s new fix closes gap that could redirect funds without stealing keys - Crypto News: Latest Cryptocurrency News and Analysis\",\"isPartOf\":{\"@id\":\"https:\/\/cryptonews.uk.com\/#website\"},\"primaryImageOfPage\":{\"@id\":\"https:\/\/cryptonews.uk.com\/?p=14062#primaryimage\"},\"image\":{\"@id\":\"https:\/\/cryptonews.uk.com\/?p=14062#primaryimage\"},\"thumbnailUrl\":\"https:\/\/cryptonews.uk.com\/wp-content\/uploads\/2026\/10\/psbt-output-check-v2.webp\",\"datePublished\":\"2026-10-04T20:20:46+00:00\",\"author\":{\"@id\":\"https:\/\/cryptonews.uk.com\/#\/schema\/person\/822778c5844e0d16d43dce6630f4f1bf\"},\"description\":\"Bitcoin Core will now refuse certain malformed PSBT signing requests where the matching transaction output is missing.\",\"breadcrumb\":{\"@id\":\"https:\/\/cryptonews.uk.com\/?p=14062#breadcrumb\"},\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"ReadAction\",\"target\":[\"https:\/\/cryptonews.uk.com\/?p=14062\"]}]},{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\/\/cryptonews.uk.com\/?p=14062#primaryimage\",\"url\":\"https:\/\/cryptonews.uk.com\/wp-content\/uploads\/2026\/10\/psbt-output-check-v2.webp\",\"contentUrl\":\"https:\/\/cryptonews.uk.com\/wp-content\/uploads\/2026\/10\/psbt-output-check-v2.webp\",\"width\":1280,\"height\":720},{\"@type\":\"BreadcrumbList\",\"@id\":\"https:\/\/cryptonews.uk.com\/?p=14062#breadcrumb\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"https:\/\/cryptonews.uk.com\/\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"Bitcoin Core\u2019s new fix closes gap that could redirect funds without stealing keys\"}]},{\"@type\":\"WebSite\",\"@id\":\"https:\/\/cryptonews.uk.com\/#website\",\"url\":\"https:\/\/cryptonews.uk.com\/\",\"name\":\"Crypto News: Latest Cryptocurrency News and Analysis\",\"description\":\"Latest Crypto &amp; 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