libcurl

About this tag
The libcurl tag on WindowsForum.com covers security vulnerabilities and technical discussions related to the libcurl networking library, which is widely embedded in open-source and enterprise software. Recent threads focus on CVEs disclosed in 2023 and 2026, including connection reuse flaws, authentication bypasses, HSTS concurrency bugs, and credential leaks. Topics also address patching strategies, vendor attestations (e.g., Azure Linux), and practical mitigation steps for administrators. The content is relevant for IT professionals, developers, and system administrators who manage systems relying on libcurl for HTTP, FTP, or other protocol transfers.

  1. CVE-2026-3784: Curl Proxy Connect Reuse Flaw Fixed in curl 8.19.0

    The curl project disclosed a new vulnerability, tracked as CVE-2026-3784, in which libcurl and the curl command-line tool can wrongly reuse an existing HTTP proxy connection established with one set of proxy credentials when a subsequent request attempts to use different proxy credentials — a...
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    • curl security cve 2026 3784 libcurl proxy authentication
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  2. CVE-2026-1965: libcurl Negotiate auth flaw fixed in 8.19.0

    libcurl's Negotiate authentication code has a logic flaw that can cause a request to reuse a connection authenticated for a different user, exposing authenticated sessions to wrong-identity reuse and credential confusion — a vulnerability tracked as CVE-2026-1965 that was disclosed and fixed by...
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    • cve 2026 1965 libcurl negotiate authentication session reuse
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  3. CVE-2026-3783: Curl Bearer Token Leak via .netrc Redirects Fixed in 8.19.0

    A newly disclosed flaw, tracked as CVE-2026-3783, allows an OAuth2 bearer token to be unintentionally forwarded across HTTP(S) redirects when cURL or libcurl is instructed to use credentials from a user .netrc file — potentially exposing sensitive access tokens to attacker-controlled hosts. The...

  4. CVE-2023-27537: Libcurl HSTS Concurrency Bug and Patch Guide

    A concurrency flaw in libcurl’s HSTS sharing code can cause a double-free or use-after-free when two threads share the same HSTS storage, producing crashes and availability failures for affected applications; the bug was disclosed as CVE-2023-27537 and addressed by the curl project and...
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    • concurrency bug hsts sharing libcurl vendor patching
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  5. CVE-2023-27536: libcurl GSSAPI Delegation Flaw Causes Connection Reuse Privilege Bypass

    A subtle connection-reuse bug in libcurl—tracked as CVE-2023-27536—exposed a real-world risk that the library could accidentally reuse an authenticated connection with higher GSSAPI/Kerberos delegation permissions for a subsequent transfer that should have been performed with lower permissions...
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    • authentication bypass cve 2023 27536 gssapi delegation libcurl
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  6. Understanding CVE-2023-27538: Azure Linux Attestation and libcurl Risk

    The short answer is: Microsoft’s MSRC advisory naming Azure Linux as a carrier of the vulnerable libcurl component is an authoritative, product‑scoped attestation — but it is not a technical guarantee that Azure Linux is the only Microsoft product that could include libcurl and therefore be...

  7. CVE-2024-6874 Explained: macidn Bug in libcurl and Azure Linux Attestations

    The macidn/punycode bug tracked as CVE-2024-6874 is real, but the short answer to the question is: Microsoft’s public attestation names Azure Linux as the product that includes the affected upstream component, but that attestation is an inventory statement — not proof that no other Microsoft...
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    • azure linux cybersecurity libcurl vulnerability attestations
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  8. CVE-2023-38546: libcurl Cookie Duplication Bug and Patch 8.4.0

    A subtle bug in libcurl’s handle-duplication logic can let an attacker plant cookies into a running process under a narrow set of conditions — a reliability bug that turned into a security issue and was assigned CVE‑2023‑38546. The flaw is small in scope, rated low severity by the curl project...
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    • cookie security dup handle libcurl security vulnerability
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  9. CVE-2024-2398: Curl HTTP/2 Push Memory Leak and Azure Linux Attestation

    The curl project’s advisory for CVE-2024-2398 describes a straightforward but consequential bug: when an application enables HTTP/2 server push, libcurl can leak previously allocated header memory if a pushed stream exceeds the library’s header limit and is aborted — a leak that can amount to...

  10. CVE-2025-10148: Azure Linux Attestation and curl Libcurl Risk

    The recently assigned CVE-2025-10148 — a predictable WebSocket mask bug in curl/libcurl — is real, it is patched upstream, and Microsoft’s short public attestation that “Azure Linux includes this open‑source library and is therefore potentially affected” is accurate for the product it covers...
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    • azure linux curl vulnerability libcurl vex csaf attestations
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    • Forum: Security Alerts

  11. CVE-2025-9086: libcurl cookie path off-by-one read causes crashes and cookie override risk

    A silent boundary-check mistake in a widely used networking library has resurfaced a familiar security lesson: small parsing errors in C can still bite large ecosystems. In September 2025 the curl project disclosed CVE-2025-9086, an out-of-bounds read in cookie path handling inside libcurl that...
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    • libcurl memory safety web security windows security
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