How should we interpret CVSS severity scores?

CVSS estimates technical severity, but it does not automatically equal business risk. Prioritize using context like internet exposure, asset criticality, known exploitation, and whether compensating controls exist. A Medium CVSS on an exposed production system can be more urgent than a Critical on an isolated non-production host.

Vulnerability Database

Q: What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

Q: What's the difference between a vulnerability, an exploit, and a zero-day?

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. Risk increases sharply when exploitation becomes reliable or widespread.

Q: Why do vulnerabilities keep reappearing in our environment?

Recurring findings usually come from incomplete asset discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host.

Q: How do we prioritize remediation without burning out the team?

Use a repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress so remediation is steady, not reactive.

Q: How can SynScan help reduce vulnerability risk over time?

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.

362,557

Total vulnerabilities in the database

Guzzle: Host-only cookie scope is not preserved — guzzlehttp / guzzle

Insertion of Sensitive Information Into Sent Data

Impact

In affected versions, CookieJar does not preserve whether a response cookie was set without a Domain attribute or with an empty one. A cookie without Domain is host-only and must be returned only to the exact host that set it. Under current cookie processing rules, an empty Domain value is also host-only. Guzzle instead stores the request host in the cookie's Domain field and later applies ordinary domain matching, as though the server had supplied a valid domain. For example, a host-only sid=secret cookie set by example.com can subsequently be sent to child.example.com. FileCookieJar and SessionCookieJar also persist the request host without recording the host-only state, so reloading a jar preserves the widened scope.

An attacker who controls or can observe a child host can therefore receive cookies that were intended only for its parent host. Depending on the cookie, this can disclose session identifiers, authorization tokens, or other sensitive state. Exploitation requires the application to enable Guzzle's cookie support, reuse the same built-in cookie jar, receive a host-only cookie from a parent host, and later make a matching request to a less-trusted child host. The cookie's other restrictions still apply. Its path must match, a Secure cookie is sent only over a secure connection, and an expired cookie is not sent.

Applications that do not use Guzzle's cookie support are not affected. Applications are also not affected by this disclosure if they use a separate jar for every host or trust boundary, never request a less-trusted subdomain with the same jar, or only store cookies carrying a valid, non-empty Domain attribute. The incorrect behavior occurs between an otherwise valid parent host and its subdomains.

Patches

The issue is patched in 7.15.1 and later. Starting in that release, Guzzle records whether a response cookie is host-only and matches it only against the exact host. The host-only flag is part of cookie identity for replacement and response-driven deletion. Cookies carrying a valid, non-empty Domain attribute retain their existing domain-matching behavior. A host-only cookie can coexist with an explicit-domain cookie having the same name, domain string, and path.

The built-in persistent jars now write a boolean HostOnly marker for every stored cookie record. They reject records where that marker is missing or is not a boolean, and validate all records before changing the live jar. Persisted cookie records written by an older version are therefore rejected rather than silently interpreted with an unsafe scope. Loading non-empty file or session data written without this marker throws a RuntimeException until the data is deleted, regenerated, or correctly annotated. Versions before 7.15.1 are affected.

Workarounds

If you cannot upgrade immediately, do not reuse one CookieJar instance across parent and child hosts with different trust levels. Use a separate cookie jar for each host or trust boundary, disable cookie handling for requests to less-trusted hosts, or avoid making those requests through a client configured with a shared jar. In particular, avoid new Client(['cookies' => true]) for a client that may contact both a trusted parent host and less-trusted subdomains, because that option creates one jar for the whole client.

When upgrading, delete or rotate existing FileCookieJar and SessionCookieJar data that contains cookie records written without a HostOnly marker. Records may instead be annotated manually only when the original presence or absence of the cookie's Domain attribute is known. The stored domain string is not sufficient to infer it safely.

References

https://www.rfc-editor.org/rfc/rfc10025.html#section-4.1.2.3
https://www.rfc-editor.org/rfc/rfc10025.html#section-5.7
https://www.rfc-editor.org/rfc/rfc10025.html#section-5.8.3

Published: Jul 20, 2026
Updated: Jul 21, 2026
GHSA: GHSA-wm3w-8rrp-j577
Severity: Medium
Exploit:
CISA KEV:

CVSS v3:

Severity: Medium
Score: 5.9
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

CWEs:

Affected Software
References

Software	From	Fixed in
guzzlehttp / guzzle	-	7.15.1

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Frequently Asked Questions

What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.