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curl EUVDEUVD-2026-29922

| CVE-2026-4873 MEDIUM
Cleartext Transmission of Sensitive Information (CWE-319)
5.9
CVSS 3.1 · Vendor
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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Access
    Establish MitM position on network path
  2. Delivery
    Observe curl session initiating HTTP connection to target host
  3. Exploit
    Wait for plaintext connection to persist in curl pool
  4. Execution
    Trigger or await HTTPS request to same host
  5. Persist
    curl reuses cleartext connection, bypassing TLS
  6. Impact
    Intercept sensitive data transmitted in plaintext

Vulnerability Assessment

Weakness
CWE
OWASP Top 10:2025
A04:2025 - Cryptographic Failures
ASVS 5.0
V12 - Secure Communication Transport encryption
Exploitation Conditions

The vulnerability triggers when curl's connection pool contains an existing plaintext (non-TLS) connection to a host at the moment a new HTTPS request targeting that same host is issued within the same curl session or multi-handle. This requires two specific concurrent conditions: (1) a prior HTTP request to the same host must have left a reusable connection in the pool - meaning the previous connection is still open and not expired - and (2) a subsequent HTTPS request to that same host is made before the plaintext connection times out. Exploitation is further constrained by the requirement that the attacker have a network-level interception position (man-in-the-middle) to observe or manipulate the cleartext traffic; the flaw itself does not provide remote code execution or network access. Unauthenticated network access is confirmed per CVSS PR:N, but this refers to curl's own authentication, not the attacker's position. Scenarios most at risk are server-side applications that make both HTTP and HTTPS requests to the same remote host within a single connection pool, such as redirect-following or mixed-scheme API integrations.

Impact

The CVSS 5.9 with vector AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N presents a nuanced risk profile. High confidentiality impact (C:H) reflects that the full contents of requests - including bearer tokens, API keys, and session credentials - can be exposed. However, AC:H (high attack complexity) materially constrains exploitability, requiring a specific connection pool state (a reusable plaintext connection present at the moment an HTTPS request is made) and a network-level interception position. EPSS at 0.01% (2nd percentile) and SSVC exploitation: none with automatable: no directly corroborate this constraint - the conditions are too specific for opportunistic mass exploitation. This is not in CISA KEV and no POC is publicly known. The combination of high data sensitivity impact but low exploitation probability places this as a normal-cycle patch priority: high urgency for environments where curl handles authentication flows (OAuth, API integrations, CI/CD credential injection), but not an emergency requiring out-of-band patching for general deployments. The simultaneous disclosure of two related flaws (CVE-2026-5545, CVE-2026-5773) strengthens the case for prompt patching of the entire curl release.

Exploit ScenarioDerived

An attacker positioned as a man-in-the-middle on the network path - for example, on a shared network segment, a compromised router, or via ARP poisoning - waits for a curl session that has established a plaintext HTTP connection to a target host. When curl subsequently issues an HTTPS request to the same host and erroneously reuses the existing cleartext connection due to the TLS enforcement flaw, the attacker intercepts the plaintext traffic and captures sensitive headers such as Authorization bearer tokens or Set-Cookie values. No public proof-of-concept is known at time of analysis; the AC:H CVSS rating reflects that the attacker must both have network interception capability and induce the specific connection pool state required to trigger the reuse.

This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).
Patch available 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – Jun 08, 2026

Connection reuse logic in curl ignores TLS requirements, causing sensitive data to be transmitted in cleartext over channels that should be TLS-encrypted. When curl's connection pool reuses an existing non-encrypted connection to fulfill a subsequent HTTPS request, credentials, tokens, or request payloads may traverse the network without encryption. Affects curl versions 7.20.0 through 8.19.0 (cpe:2.3:a:haxx:curl); no public exploit is identified at time of analysis, SSVC confirms exploitation: none, and EPSS stands at 0.01% (2nd percentile).

RemediationAI

Vendor-released patch is confirmed available per the curl official security advisory at https://curl.se/docs/CVE-2026-4873.html; the exact fixed release version number is not specified in the available input data and should be verified directly at that URL before deployment. Red Hat users should apply RHSA-2026:12916 via 'yum update curl' or equivalent package management. SUSE users should apply the appropriate update among SUSE-SU-2026:1717, SUSE-SU-2026:1940, SUSE-SU-2026:21440, or SUSE-SU-2026:21452 depending on their SUSE Linux Enterprise product version. As a compensating control where patching is not immediately feasible, libcurl application developers can set CURLOPT_FORBID_REUSE=1 to force a new connection for each transfer, preventing connection pool reuse entirely - this eliminates the vulnerability but imposes additional TLS handshake latency and connection overhead per request. Command-line curl users can use '--no-keepalive' to achieve similar isolation. Environments running curl within CI/CD pipelines or automated credential-exchange workflows should prioritize patching given the data sensitivity risk.

Affected VersionsENISA

curl 7.28.1 ≤7.28.1
curl 8.2.1 ≤8.2.1
curl 7.49.1 ≤7.49.1
curl 7.44.0 ≤7.44.0
curl 7.83.1 ≤7.83.1
curl 7.33.0 ≤7.33.0
curl 7.32.0 ≤7.32.0
curl 7.68.0 ≤7.68.0
curl 7.88.1 ≤7.88.1
curl 7.31.0 ≤7.31.0
curl 7.50.2 ≤7.50.2
curl 7.71.1 ≤7.71.1
curl 7.51.0 ≤7.51.0
curl 7.78.0 ≤7.78.0
curl 8.1.0 ≤8.1.0
curl 7.50.0 ≤7.50.0
curl 7.26.0 ≤7.26.0
curl 7.66.0 ≤7.66.0
curl 7.65.1 ≤7.65.1
curl 7.23.1 ≤7.23.1
curl 7.79.0 ≤7.79.0
curl 7.37.0 ≤7.37.0
curl 7.71.0 ≤7.71.0
curl 7.50.1 ≤7.50.1
curl 7.65.3 ≤7.65.3
curl 7.43.0 ≤7.43.0
curl 7.21.2 ≤7.21.2
curl 8.3.0 ≤8.3.0
curl 7.62.0 ≤7.62.0
curl 8.18.0 ≤8.18.0
curl 7.53.1 ≤7.53.1
curl 7.37.1 ≤7.37.1
curl 7.75.0 ≤7.75.0
curl 7.55.1 ≤7.55.1
curl 7.36.0 ≤7.36.0
curl 7.52.0 ≤7.52.0
curl 7.23.0 ≤7.23.0
curl 7.76.1 ≤7.76.1
curl 7.63.0 ≤7.63.0
curl 7.46.0 ≤7.46.0
curl 7.21.6 ≤7.21.6
curl 8.9.1 ≤8.9.1
curl 7.61.1 ≤7.61.1
curl 7.70.0 ≤7.70.0
curl 8.15.0 ≤8.15.0
curl 8.19.0 ≤8.19.0
curl 7.29.0 ≤7.29.0
curl 7.73.0 ≤7.73.0
curl 7.40.0 ≤7.40.0
curl 7.20.0 ≤7.20.0
curl 7.76.0 ≤7.76.0
curl 7.74.0 ≤7.74.0
curl 8.11.1 ≤8.11.1
curl 7.57.0 ≤7.57.0
curl 7.42.1 ≤7.42.1
curl 7.41.0 ≤7.41.0
curl 7.50.3 ≤7.50.3
curl 7.21.0 ≤7.21.0
curl 7.21.3 ≤7.21.3
curl 7.60.0 ≤7.60.0
curl 7.42.0 ≤7.42.0
curl 7.58.0 ≤7.58.0
curl 7.25.0 ≤7.25.0
curl 8.7.1 ≤8.7.1
curl 7.28.0 ≤7.28.0
curl 7.64.0 ≤7.64.0
curl 7.21.5 ≤7.21.5
curl 7.22.0 ≤7.22.0
curl 8.1.1 ≤8.1.1
curl 7.47.0 ≤7.47.0
curl 7.53.0 ≤7.53.0
curl 8.17.0 ≤8.17.0
curl 7.48.0 ≤7.48.0
curl 7.30.0 ≤7.30.0
curl 7.81.0 ≤7.81.0
curl 8.16.0 ≤8.16.0
curl 7.47.1 ≤7.47.1
curl 7.24.0 ≤7.24.0
curl 7.84.0 ≤7.84.0
curl 7.56.1 ≤7.56.1
curl 8.14.0 ≤8.14.0
curl 7.88.0 ≤7.88.0
curl 8.0.0 ≤8.0.0
curl 8.10.0 ≤8.10.0
curl 7.54.0 ≤7.54.0
curl 8.12.0 ≤8.12.0
curl 7.21.1 ≤7.21.1
curl 7.39.0 ≤7.39.0
curl 7.87.0 ≤7.87.0
curl 7.69.1 ≤7.69.1
curl 7.82.0 ≤7.82.0
curl 7.35.0 ≤7.35.0
curl 7.83.0 ≤7.83.0
curl 7.45.0 ≤7.45.0
curl 8.13.0 ≤8.13.0
curl 7.72.0 ≤7.72.0
curl 7.38.0 ≤7.38.0
curl 8.11.0 ≤8.11.0
curl 8.12.1 ≤8.12.1
curl 8.10.1 ≤8.10.1
curl 7.65.2 ≤7.65.2
curl 7.77.0 ≤7.77.0
curl 7.61.0 ≤7.61.0
curl 8.0.1 ≤8.0.1
curl 7.69.0 ≤7.69.0
curl 7.79.1 ≤7.79.1
curl 7.55.0 ≤7.55.0
curl 7.86.0 ≤7.86.0
curl 7.52.1 ≤7.52.1
curl 8.6.0 ≤8.6.0
curl 7.65.0 ≤7.65.0
curl 8.5.0 ≤8.5.0
curl 7.54.1 ≤7.54.1
curl 7.85.0 ≤7.85.0
curl 7.49.0 ≤7.49.0
curl 7.56.0 ≤7.56.0
curl 7.59.0 ≤7.59.0
curl 8.14.1 ≤8.14.1
curl 7.20.1 ≤7.20.1
curl 7.67.0 ≤7.67.0
curl 7.80.0 ≤7.80.0
curl 8.8.0 ≤8.8.0
curl 8.7.0 ≤8.7.0
curl 7.21.7 ≤7.21.7
curl 8.4.0 ≤8.4.0
curl 7.64.1 ≤7.64.1
curl 7.27.0 ≤7.27.0
curl 8.2.0 ≤8.2.0
curl 7.21.4 ≤7.21.4
curl 8.1.2 ≤8.1.2
curl 8.9.0 ≤8.9.0
curl 7.34.0 ≤7.34.0

Affected Packages

euvd curl no fix

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 1 package in euvd

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

curl's connection reuse subsystem - a performance optimization that keeps established connections alive and reuses them for subsequent requests to the same host - fails to validate that a pooled connection satisfies the TLS requirements of an incoming request. CWE-319 (Cleartext Transmission of Sensitive Information) identifies the root cause: sensitive data is transmitted over a channel that should be encrypted but is not, because the connection selection logic does not enforce protocol-level security constraints before reuse. The affected product is cpe:2.3:a:haxx:curl:*:*:*:*:*:*:*:* spanning versions 7.20.0 through 8.19.0 per EUVD data, indicating this logic flaw has existed across approximately 15 years of releases. This advisory is one of three related curl connection reuse flaws disclosed simultaneously by Daniel Stenberg (CVE-2026-4873, CVE-2026-5545 for HTTP Negotiate, CVE-2026-5773 for SMB), suggesting a systemic pattern in how curl's connection pool validates protocol security requirements. Note: the 'Buffer Overflow' tag present in the intelligence source is inconsistent with CWE-319 and the CVE description; it should be treated as a data quality artifact in that source and does not reflect the actual vulnerability class.

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Severity by source

Vendor (CNA) PRIMARY 5.9 MEDIUM
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
SUSE MEDIUM
Red Hat 5.3 MEDIUM

Primary rating from Vendor (CNA).

CVSS VectorVendor

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

Lifecycle Timeline

2
CVSS changed
May 13, 2026 - 20:22 NVD
5.9 (MEDIUM)
CVE Published
May 08, 2026 - 06:45 nvd
UNKNOWN (no severity yet)

Description PRE-NVD

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

Threat Intelligence Overview

EPSS Score
0.0%
Top 98% exploitable
Social Media
2
Sightings
Data Quality
7 sources
Confidence: High

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity MEDIUM
CISA KEV No
Public POC No
EPSS 0.0%
Patch available Yes
Active threat No
Deciding rule
MEDIUM severity (CVSS 4.0-6.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Scheduled
Exploitation
None
System Exposure· derived
Open
Automatable
No
Human Impact· derived
Medium
Technical Impact
Partial

Priority Score

30
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +30
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.

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Vendor StatusVendor

SUSE

Severity: Medium
Product Status
Container suse/manager/4.3/proxy-httpd:4.3.17.9.76.18 Container suse/manager/4.3/proxy-salt-broker:4.3.17.9.66.20 Container suse/sle-micro-rancher/5.3:latest Container suse/sle-micro-rancher/5.4:5.4.4.5.106 Container suse/sle-micro/5.3/toolbox:16.3-6.11.222 Container suse/sle-micro/5.4/toolbox:16.3-5.19.222 Container suse/sle-micro/5.5/toolbox:16.3-3.12.133 Container suse/sle-micro/base-5.5:2.0.4-5.8.271 Image SLES15-SP4-BYOS Image SLES15-SP4-BYOS-Azure Image SLES15-SP4-BYOS-EC2 Image SLES15-SP4-BYOS-GCE Image SLES15-SP4-CHOST-BYOS Image SLES15-SP4-CHOST-BYOS-Aliyun Image SLES15-SP4-CHOST-BYOS-Azure Image SLES15-SP4-CHOST-BYOS-EC2 Image SLES15-SP4-CHOST-BYOS-GCE Image SLES15-SP4-CHOST-BYOS-SAP-CCloud Image SLES15-SP4-HPC-BYOS Image SLES15-SP4-HPC-BYOS-Azure Image SLES15-SP4-HPC-BYOS-EC2 Image SLES15-SP4-HPC-BYOS-GCE Image SLES15-SP4-HPC-EC2 Image SLES15-SP4-HPC-GCE Image SLES15-SP4-Hardened-BYOS Image SLES15-SP4-Hardened-BYOS-Azure Image SLES15-SP4-Hardened-BYOS-EC2 Image SLES15-SP4-Hardened-BYOS-GCE Image SLES15-SP4-SAP-BYOS Image SLES15-SP4-SAP-BYOS-Azure Image SLES15-SP4-SAP-BYOS-EC2 Image SLES15-SP4-SAP-BYOS-GCE Image SLES15-SP4-SAP-Hardened Image SLES15-SP4-SAP-Hardened-Azure Image SLES15-SP4-SAP-Hardened-BYOS Image SLES15-SP4-SAP-Hardened-BYOS-Azure Image SLES15-SP4-SAP-Hardened-BYOS-EC2 Image SLES15-SP4-SAP-Hardened-BYOS-GCE Image SLES15-SP4-SAP-Hardened-GCE Image SLES15-SP5-BYOS-Azure Image SLES15-SP5-BYOS-EC2 Image SLES15-SP5-BYOS-GCE Image SLES15-SP5-CHOST-BYOS-Aliyun Image SLES15-SP5-CHOST-BYOS-Azure Image SLES15-SP5-CHOST-BYOS-EC2 Image SLES15-SP5-CHOST-BYOS-GCE Image SLES15-SP5-CHOST-BYOS-GDC Image SLES15-SP5-CHOST-BYOS-SAP-CCloud Image SLES15-SP5-EC2 Image SLES15-SP5-GCE Image SLES15-SP5-HPC-BYOS-Azure Image SLES15-SP5-HPC-BYOS-EC2 Image SLES15-SP5-HPC-BYOS-GCE Image SLES15-SP5-Hardened-BYOS-Azure Image SLES15-SP5-Hardened-BYOS-EC2 Image SLES15-SP5-Hardened-BYOS-GCE Image SLES15-SP5-SAP-Azure-3P Image SLES15-SP5-SAP-BYOS-Azure Image SLES15-SP5-SAP-BYOS-EC2 Image SLES15-SP5-SAP-BYOS-GCE Image SLES15-SP5-SAP-Hardened-Azure Image SLES15-SP5-SAP-Hardened-BYOS-Azure Image SLES15-SP5-SAP-Hardened-BYOS-EC2 Image SLES15-SP5-SAP-Hardened-BYOS-GCE Image SLES15-SP5-SAP-Hardened-GCE Affected
Container suse/sl-micro/6.0/baremetal-os-container:2.1.3-6.172 Container suse/sl-micro/6.0/kvm-os-container:2.1.3-6.155 Container suse/sl-micro/6.0/rt-os-container:2.1.3-7.168 Affected
Container suse/sl-micro/6.0/base-os-container:2.1.3-7.139 Container suse/sl-micro/6.0/toolbox:13.2-9.105 Image SL-Micro Affected
Container suse/sl-micro/6.1/baremetal-os-container:2.2.1-7.102 Container suse/sl-micro/6.1/kvm-os-container:2.2.1-5.127 Container suse/sl-micro/6.1/rt-os-container:2.2.1-5.116 Affected
Container suse/sl-micro/6.1/base-os-container:2.2.1-5.126 Image SL-Micro-Azure Image SL-Micro-BYOS-Azure Image SL-Micro-BYOS-EC2 Image SL-Micro-BYOS-GCE Image SL-Micro-EC2 Image SUSE-Multi-Linux-Manager-Proxy-BYOS-Azure Image SUSE-Multi-Linux-Manager-Proxy-BYOS-EC2 Image SUSE-Multi-Linux-Manager-Proxy-BYOS-GCE Image SUSE-Multi-Linux-Manager-Server-Azure-llc Image SUSE-Multi-Linux-Manager-Server-Azure-ltd Image SUSE-Multi-Linux-Manager-Server-BYOS-Azure Image SUSE-Multi-Linux-Manager-Server-BYOS-EC2 Image SUSE-Multi-Linux-Manager-Server-BYOS-GCE Image SUSE-Multi-Linux-Manager-Server-EC2-llc Image SUSE-Multi-Linux-Manager-Server-EC2-ltd Affected

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