CVE-2026-48998 is a medium-severity improper input validation vulnerability in guzzlehttp/psr7 (composer), affecting versions < 2.10.2. It is fixed in 2.10.2.
Impact guzzlehttp/psr7 improperly interpreted malformed Host header values when constructing request URIs from inbound request data. This issue concerns inbound request parsing and server request construction. It does not require serializing a PSR-7 request, and it is not part of the normal outbound request-sending path used by guzzlehttp/guzzle. A vulnerable flow is: An attacker controls a raw HTTP request or server variable containing a Host value. The Host value contains URI authority delimiters, such as [email protected]. guzzlehttp/psr7 uses that value to construct a URI. The URI parser treats the portion before @ as userinfo and the portion after @ as the URI host. The resulting PSR-7 request URI host differs from the original Host header value. For example, Host: [email protected] can result in a PSR-7 URI whose host is evil.example, while the original Host header value remains [email protected]. Applications are affected if they parse attacker-controlled raw HTTP requests with GuzzleHttp\Psr7\Message::parseRequest() or the legacy 1.x GuzzleHttp\Psr7\parserequest() function, or if they build server requests from attacker-controlled server variables with GuzzleHttp\Psr7\ServerRequest::fromGlobals() or GuzzleHttp\Psr7\ServerRequest::getUriFromGlobals(), and then rely on the resulting URI host for routing, allow-list checks, credential selection, or forwarding decisions. Applications using guzzlehttp/psr7 only through Guzzle's standard HTTP client APIs are not expected to be affected. In affected forwarding or gateway scenarios, this may cause requests or credentials to be sent to an unintended host. Patches The issue is patched in 2.10.2 and later. 1.x is end-of-life and will not receive a patch. Workarounds If you cannot upgrade immediately, validate Host values before passing untrusted request data to Message::parseRequest(), legacy 1.x parserequest(), ServerRequest::fromGlobals(), or ServerRequest::getUriFromGlobals(). Accept only uri-host [ ":" port ]. Reject values containing whitespace, control characters, userinfo (@), path (/ or \), query (?), fragment (#), malformed IP literals or bracket syntax, or invalid port syntax. Do not validate Host by prefixing it with http:// and passing it to parse_url(), because that can reinterpret malformed values as URI userinfo and host. References https://www.rfc-editor.org/rfc/rfc9112.html#section-3.2 https://www.rfc-editor.org/rfc/rfc9112.html#section-3.3 https://www.rfc-editor.org/rfc/rfc9110.html#section-4.2.4 https://www.rfc-editor.org/rfc/rfc9110.html#section-7.2
The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.
CVE-2026-48998 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment.
A fixed version is available (2.10.2). Upgrading removes the vulnerable code path.
composer
guzzlehttp/psr7 (< 2.10.2)guzzlehttp/psr7 → 2.10.2 (composer)Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter instead of chasing every advisory.
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Upgrade guzzlehttp/psr7 to 2.10.2 or later to resolve this vulnerability.
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
CVE-2026-48998 is a medium-severity improper input validation vulnerability in guzzlehttp/psr7 (composer), affecting versions < 2.10.2. It is fixed in 2.10.2. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
CVE-2026-48998 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
guzzlehttp/psr7 (composer) versions < 2.10.2 is affected.
Yes. CVE-2026-48998 is fixed in 2.10.2. Upgrade to this version or later.
Whether CVE-2026-48998 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
Upgrade guzzlehttp/psr7 to 2.10.2 or later.