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libcurl EUVDEUVD-2026-41508

| CVE-2026-8927 CRITICAL
Authentication Bypass by Capture-replay (CWE-294)
Critical
Disputed · 9.1 Vendor
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Severity by source

Sources disagree (Medium–Critical)
Vendor (CNA) PRIMARY
9.1 CRITICAL
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
vuln.today AI
5.9 MEDIUM

Passive credential disclosure requiring reused handle, env-var proxy config, and two differing proxies drives AC:H; impact is confidentiality-only, so I:N/A:N and no scope change.

3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
4.0 AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
SUSE
5.3 MEDIUM
AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
Red Hat
7.5 HIGH
qualitative

vuln.today treats the vendor’s rating as authoritative. A higher third-party CVSS (e.g. CISA-ADP) is shown for transparency but does not drive the headline severity.

CVSS VectorVendor

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

Lifecycle Timeline

5
Analysis Updated
Jul 06, 2026 - 18:37 vuln.today
v3 (cvss_changed)
Analysis Updated
Jul 06, 2026 - 18:37 vuln.today
v2 (cvss_changed)
Re-analysis Queued
Jul 06, 2026 - 18:22 vuln.today
cvss_changed
CVSS changed
Jul 06, 2026 - 18:22 NVD
9.1 (CRITICAL)
Analysis Generated
Jun 24, 2026 - 18:25 vuln.today

Description PRE-NVD

Disclosed via oss-security. NVD scoring and full description are pending.

AnalysisAI

Proxy credential leakage in libcurl (curl) occurs when a single reused easy handle drives sequential transfers through different environment-variable-configured proxies: after Digest-authenticating to proxyA, libcurl fails to reset the proxy authentication state, so the Proxy-Authorization: header meant for proxyA is resent to proxyB. Any application relying on handle reuse with env-var proxy settings and multiple upstream proxies can disclose proxyA's credentials to an unauthorized proxy operator. EPSS is low (0.25%, 16th percentile), it is not on CISA KEV, and no public exploit identified at time of analysis - this is a credential-confidentiality issue rather than a code-execution flaw.

Technical ContextAI

libcurl is the transfer library underpinning the curl CLI and is embedded in a vast range of software, language runtimes, and appliances. The bug lives in libcurl's proxy authentication state handling: when a handle is reused (a common performance optimization to preserve connections and settings), per-request proxy auth material is not cleared before the next transfer. When proxy destinations are selected via environment variables (http_proxy/https_proxy/etc.) and differ between transfers, the cached Digest Proxy-Authorization header for the previous proxy carries over. The CWE is listed as N/A upstream, but the root-cause class is CWE-200 (Exposure of Sensitive Information) combined with CWE-212 (Improper Removal of Sensitive Information before reuse) - sensitive per-authority state is not sanitized across a state boundary. Because it is a Digest header (not Basic), the leaked value is a response hash tied to a challenge, but it still discloses that credentials exist for proxyA and can aid credential attacks against the intended proxy.

RemediationAI

Patch available per vendor advisory - upgrade libcurl/curl to the fixed release published by the curl project (see https://curl.se/docs/CVE-2026-8927.html; the exact patched version is not stated in the provided data and should be confirmed against that advisory) and apply your distribution's update, e.g. Ubuntu via USN-8487-1 (https://ubuntu.com/security/notices/USN-8487-1). Until patched, the most direct compensating control is to avoid reusing a single libcurl handle across transfers that target different proxies - create a fresh handle per proxy destination or explicitly clear proxy auth (reset CURLOPT_PROXYUSERPWD / disable proxy Digest) between transfers, which costs some connection-reuse efficiency. Alternatively, stop relying on environment-variable proxy configuration for multi-proxy workflows and set the proxy explicitly per request, or route all traffic through a single trusted proxy so no cross-proxy leak is possible; both reduce flexibility but eliminate the leak path.

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Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
SLES15-SP5-CHOST-BYOS-SAP-CCloud Affected
SLES15-SP6-CHOST-BYOS Affected
SLES15-SP6-CHOST-BYOS-Aliyun Affected
SLES15-SP6-CHOST-BYOS-Azure Affected
SLES15-SP6-CHOST-BYOS-EC2 Affected

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EUVD-2026-41508 vulnerability details – vuln.today

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