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CVE-2026-6276— stale custom cookie host causes cookie leak

Quick assessment

Affected
curl curl
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

libcurl是cURL开源的一个免费且易于使用的客户端 URL 传输库。 libcurl存在安全漏洞，该漏洞源于自定义Host标头处理不当，可能导致第二次请求时错误传递第一次请求的Cookie。

AI Predicted 7.5 Difficulty: Moderate EPSS 0.35% · P26

Possible ATT&CK Techniques 1 AI

T1530 · Data from Cloud Storage

Affected Version Matrix 57

VendorProduct Version RangeStatus
curl curl 7.71.0< 8.14.2 affected
8.15.0< 8.16.1 affected
8.17.0< 8.20.0 affected
e15e51384a423be31318b3c9c7d612a1aae661fd< 3a19987a87f393d9394fe5acc7643f6c263c92db affected
8.19.0 affected
8.18.0 affected
8.17.0 affected
8.16.0 affected
… +49 more rows
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I. Basic Information for CVE-2026-6276

Vulnerability Information
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Vulnerability Title
stale custom cookie host causes cookie leak
Source: CVE Program / CVE List V5
Vulnerability Description
Using libcurl, when a custom `Host:` header is first set for an HTTP request and a second request is subsequently done using the same *easy handle* but without the custom `Host:` header set, the second request would use stale information and pass on cookies meant for the first host in the second request. Leak them.
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
源验证错误
Source: CVE Program / CVE List V5
Vulnerability Title
libcurl 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
libcurl是cURL开源的一个免费且易于使用的客户端 URL 传输库。 libcurl存在安全漏洞，该漏洞源于自定义Host标头处理不当，可能导致第二次请求时错误传递第一次请求的Cookie。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
curl curl 7.71.0 ~ 8.14.2 -
curl curl e15e51384a423be31318b3c9c7d612a1aae661fd ~ 3a19987a87f393d9394fe5acc7643f6c263c92db -
curl curl 8.19.0 -

II. Public POCs for CVE-2026-6276

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III. Intelligence Information for CVE-2026-6276

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Vendor Advisories for CVE-2026-6276 (2)

Other References for CVE-2026-6276 (1)

Same Patch Batch · curl · 2026-05-13 · 8 CVEs total

CVE-2026-7168 cross-proxy Digest auth state leak
CVE-2026-7009 OCSP stapling bypass with Apple SecTrust
CVE-2026-6253 proxy credentials leak over redirect-to proxy
CVE-2026-6429 netrc credential leak with reused proxy connection
CVE-2026-4873 connection reuse ignores TLS requirement
CVE-2026-5545 wrong reuse of HTTP Negotiate connection
CVE-2026-5773 wrong reuse of SMB connection

IV. Related Vulnerabilities

Same product: curl
Same vendor: curl
Same weakness: CWE-346

V. Comments for CVE-2026-6276

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