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

Exp

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.

Published: 2026-05-13 Last update: 2026-05-14 Assigner: 2499f714-1537-4658-8207-48ae4bb9eae9 Source: 2499f714-1537-4658-8207-48ae4bb9eae9
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-6276 is rated Exploit Available (50/100): CVSS High severity, with low exploitation likelihood (EPSS 0.01%). 1 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2026-6276

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2026-6276

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-05-13 — 0.01% —

Full EPSS history (1 record total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-6276

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 134c704f-9b21-4f2e-91b3-4a467353bcc0

Weakness enumeration for CVE-2026-6276

GitHub Security Advisory for CVE-2026-6276

GHSA-2jc6-hc33-hv48 · Severity: high — Using libcurl, when a custom `Host:` header is first set for an HTTP request and a second request...

OS Trackers for CVE-2026-6276

vendor priority summary link
debian not yet assigned CVE-2026-6276 not yet assigned priority: Debian including 1 source packages (curl), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): open 3, resolved 2. https://security-tracker.debian.org/tracker/CVE-2026-6276
redhat low — https://access.redhat.com/security/cve/CVE-2026-6276
suse low CVE-2026-6276 severity low: SUSE including 12 source package names (curl, curl-8.14.1-150400.5.83.1, …), 73 product×package rows across 23 product lines (SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS, SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS, … (23 product lines)): First Fixed 64, Known Not Affected 9. https://www.suse.com/security/cve/CVE-2026-6276/
ubuntu low CVE-2026-6276 low priority: Ubuntu including 1 source packages (curl), 9 status rows across 9 suites (bionic, focal, jammy, noble, questing, resolute, trusty, upstream, xenial): not-affected 4, released 4, pending 1. https://ubuntu.com/security/CVE-2026-6276

Affected software / configurations for CVE-2026-6276

Vendor Product Version Raw CPE
haxx curl >= 7.71.0, < 8.20.0 cpe:2.3:a:haxx:curl:*:*:*:*:*:*:*:*

References for CVE-2026-6276

URL Tags
https://curl.se/docs/CVE-2026-6276.html Patch Vendor Advisory
https://curl.se/docs/CVE-2026-6276.json Product
https://hackerone.com/reports/3671818 Exploit Issue Tracking Third Party Advisory
http://www.openwall.com/lists/oss-security/2026/04/29/13 Mailing List Third Party Advisory
cvelogic Threat Intelligence