7.5High

CVE-2026-9546sending old referer

curl curl Published: 2026-07-03 09:18 (4 months ago)

Description

A vulnerability in libcurl caused the HTTP `Referer:` header to persist even when explicitly cleared. While the documentation states that passing NULL to `CURLOPT_REFERER` suppresses the header, the option failed to clear the internal state. As a result, the previous referrer string was erroneously reused and sent in subsequent requests, potentially leaking sensitive information to unintended servers.

Weakness (CWE): CWE-200

Data: CVE.org, NVD, CISA KEV, FIRST EPSS, Ubuntu. Published as the sources state it, in English.

Affected products and versions

Vendor	Product	Versions
curl	curl	8.18.0 – < 8.20.1
haxx	curl	8.18.0 – < 8.21.0

References and patches

https://curl.se/docs/CVE-2026-9546.json Third Party Advisory
https://curl.se/docs/CVE-2026-9546.html PatchVendor Advisory
https://hackerone.com/reports/3754343 ExploitIssue TrackingThird Party Advisory

CPE matches (NVD) (1)

cpe:2.3:a:haxx:curl:*:*:*:*:*:*:*:* ≥ 8.18.0 < 8.21.0

CVSS score

7.5High

Source: CISA-ADP · CVSS 3.1

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: None
Availability: None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

All scores (2)

CISA-ADP	CVSS 3.1	7.5High
134c704f-9b21-4f2e-91b3-4a467353bcc0	CVSS 3.1	7.5High

EPSS (chance of exploitation in 30 days)

0.65%

higher than 52% of all CVEs

CISA assessment (SSVC)

Exploitation: poc
Automatable: yes
Technical impact: partial

Timeline

ID reserved2026-05-26
Published2026-07-03 09:18
Reached IP-DB2026-10-24 23:46
Last updated2026-09-15 10:16

Assigned by (CNA): curl
NVD status: Modified

View at source: CVE.org · NVD

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