High Cryptography exploit reference

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

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 May 13, 2026 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: curl

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

EPSS 0.3% (30-day exploitation probability)+4
Technical severity (high)+6
CISA SSVC: exploitation "poc"+5
Automatable exploitation (SSVC)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

0.35%

ahead of 27% of scored CVEs · Oct 14, 2026

Affects

Curl

CVSS base

7.5

High · 3 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation

Proof of concept

none · proof-of-concept · active

Automatable

Yes

can an attacker script the kill-chain steps

Technical impact

Partial

partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

Documented patch — curl.se (NIST National Vulnerability Database)

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Curl Curl, Haxx Curl).
The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
Apply the fixed version or the patch documented under Remediation.
Search available logs for exploit probes matching the vulnerability class (cryptography), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Curl	Curl	version 7.81.0version 8.1.2version 8.1.1version 8.1.0version 8.0.1version 8.0.0version 7.88.1version 7.88.0 and 49 more version 7.87.0version 7.86.0version 7.85.0version 7.84.0version 7.83.1version 7.83.0version 7.82.0version 8.2.0version 7.80.0version 7.79.1version 7.79.0version 7.78.0version 7.77.0version 7.76.1version 7.76.0version 7.75.0version 7.74.0version 7.73.0version 7.72.0version 7.71.1version 7.71.0version 8.11.1≥ 7.71.0 and < 8.14.2≥ 8.15.0 and < 8.16.1≥ 8.17.0 and < 8.20.0≥ e15e51384a423be31318b3c9c7d612a1aae661fd and < 3a19987a87f393d9394fe5acc7643f6c263c92dbversion 8.19.0version 8.18.0version 8.17.0version 8.16.0version 8.15.0version 8.14.1version 8.14.0version 8.13.0version 8.12.1version 8.12.0version 8.11.0version 8.10.1version 8.10.0version 8.9.1version 8.9.0version 8.8.0version 8.7.1version 8.7.0version 8.6.0version 8.5.0version 8.4.0version 8.3.0version 8.2.1	Vulnerable	CVE Program (cve.org) e CISA ADP
Haxx	Curl	≥ 7.71.0 and < 8.20.0	Vulnerable	NIST National Vulnerability Database

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Network

Attack complexity

Low

Privileges required

None

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
7.5	CVSS 3.1	High	3.9	3.6	nvd@nist.gov via NIST National Vulnerability Database
7.5	CVSS 3.1	High	3.9	3.6	134c704f-9b21-4f2e-91b3-4a467353bcc0 via NIST National Vulnerability Database
7.5	CVSS 3.1	High	—	—	CISA-ADP via CVE Program (cve.org) e CISA ADP

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H (score shown at the top: nvd@nist.gov)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-319 · Cleartext Transmission of Sensitive Information

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.35%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
Check TLS negotiations and unexpected certificates in the component’s traffic.

web/proxy/WAF logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first.

2026
Affected products added · curl/curl
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
SSVC assessment updated
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 13, 2026
Fix documented
Oct 13, 2026 · NIST National Vulnerability Database
CVSS changed · 7.5
Oct 13, 2026 · NIST National Vulnerability Database
Source status changed · → Modified
Oct 13, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 13, 2026 · NIST National Vulnerability Database
CVE published
May 13, 2026 · curl

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

4 on the record

curl.se/docs/CVE-2026-6276.html
Patch, Vendor Advisory, NIST National Vulnerability Database
curl.se/docs/CVE-2026-6276.json
Product, NIST National Vulnerability Database
hackerone.com/reports/3671818
Exploit, Issue Tracking, Third Party Advisory, NIST National Vulnerability Database
www.openwall.com/lists/oss-security/2026/04/29/13
Mailing List, Third Party Advisory, NIST National Vulnerability Database

Elsewhere on this site

Curl
every CVE for this vendor

Cryptography
same class

CWE-319
other pages naming this weakness

Related CVEs (same products)

High CVE-2026-92392 HTTP/2 upload Use-After-Free 1d
High CVE-2026-80229 Use After Free in Haxx Curl Sep 6, 2026
High CVE-2026-82209 Insertion of Sensitive Information Into Sent Data in Haxx Curl Sep 6, 2026
High CVE-2026-82208 Improper Certificate Validation in Haxx Curl Sep 6, 2026
High CVE-2026-80255 Insertion of Sensitive Information Into Sent Data in Haxx Curl Sep 6, 2026
High CVE-2026-80230 Improper Certificate Validation in Haxx Curl Sep 6, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-6276 is "stale custom cookie host causes cookie leak", rated High. It affects Curl (Curl); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 7.5 describes technical severity. EPSS 0.35% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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