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curl CVE-2026-9545

| EUVDEUVD-2026-41493 HIGH
2026-06-24 GHSA-6v72-wfcj-jv53
Information Disclosure Curl
7.5
CVSS 3.1 · Vendor
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Severity by source

Vendor (CNA) PRIMARY
7.5 HIGH
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
vuln.today AI
3.7 LOW

Active MITM plus non-default early-data opt-in raises complexity to AC:H; no client auth so PR:N; only request data leaks, giving C:H with I:N/A:N.

3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
4.0 AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N
SUSE
5.9 MEDIUM
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Primary rating from Vendor (CNA).

CVSS VectorVendor

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

Lifecycle Timeline

7
Analysis Updated
Jul 06, 2026 - 18:50 vuln.today
v5 (cvss_changed)
Analysis Updated
Jul 06, 2026 - 18:49 vuln.today
v4 (cvss_changed)
Analysis Updated
Jul 06, 2026 - 18:47 vuln.today
v3 (cvss_changed)
Analysis Updated
Jul 06, 2026 - 18:46 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
7.5 (HIGH)
Analysis Generated
Jun 24, 2026 - 18:26 vuln.today

Description PRE-NVD

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

Articles & Coverage 1

News Critical TLS 1.3 0-RTT Replay Vulnerability in OpenSSL - CVE-2026-9545 Jun 25, 2026

AnalysisAI

Information disclosure in libcurl (curl 8.11.0 through 8.20.0) allows a network man-in-the-middle to capture sensitive request data when TLS early data (0-RTT) is combined with SSL session ID caching. If an application enables the CURLSSLOPT_EARLYDATA bit and leaves the session cache active, libcurl can transmit a resumed request's bytes on a reconnection before it enforces a certificate verification failure, so an attacker who impersonates the original host without a valid certificate may receive the leaked data. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Establish MITM position on client's network path
Delivery
Impersonate target host without valid certificate
Exploit
Client reconnects reusing cached TLS session
Execution
libcurl sends request as 0-RTT early data
Persist
Certificate verification fails after data already sent
Impact
Attacker captures leaked sensitive request bytes
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Vulnerability AssessmentAI

Exploitation Exploitation requires all of the following to hold simultaneously: the libcurl-based application must have set the CURLSSLOPT_EARLYDATA bit in CURLOPT_SSL_OPTIONS (TLS 0-RTT is OFF by default); CURLOPT_SSL_SESSIONID_CACHE must remain enabled (the default) so a resumable session exists; and a prior successful transfer to the host must have populated the session cache. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The published CVSS 7.5 (AV:N/AC:L/PR:N/UI:N/C:H) treats this as trivially exploitable network confidentiality loss, but that score understates the real preconditions: exploitation requires (1) an application that explicitly enabled TLS early data - a non-default setting - and (2) an attacker already positioned as an active man-in-the-middle able to impersonate the target host. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An application built on libcurl enables TLS early data for performance and makes repeated requests to a host (e.g., an API endpoint) carrying authentication headers or cookies. An attacker with a network position - via ARP/DNS spoofing, rogue Wi-Fi, or route hijack - impersonates that host on the client's second connection without a valid certificate; libcurl resumes the cached session and transmits the request's 0-RTT bytes to the impostor before the certificate check aborts, leaking the sensitive headers. …
Remediation Patch available per vendor advisory - upgrade to the fixed curl/libcurl release identified at https://curl.se/docs/CVE-2026-9545.html (a released patched version tag is not independently confirmed in the input, so consult the advisory for the exact fixed version), and on Ubuntu apply the packages from USN-8487-1 (https://ubuntu.com/security/notices/USN-8487-1). … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours: Inventory all applications using libcurl versions 8.11.0-8.20.0 and determine whether CURLSSLOPT_EARLYDATA and session cache are enabled. …

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Vendor StatusVendor

SUSE

Severity: Moderate
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CVE-2026-9545 vulnerability details – vuln.today
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