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MEDIUM severity

CVE-2026-48998 — psr7

MEDIUM

CVE-2026-48998 is a medium-severity (CVSS 5.3) Improper Input Validation vulnerability in guzzlehttp/psr7. A fix is available for guzzlehttp/psr7 — see the affected versions and patch details below.

guzzlehttp/psr7 has Host Confusion via Authority Reinterpretation

Also known asGHSA-34xg-wgjx-8xph
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Oct 24, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-48998.

EPSS Exploitation Probability

via FIRST.org ↗
0.3%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs23th percentile — riskier than 23% of all scored CVEsHighest risk
0.00%0.27%0.54%0.81%0.2%0.2%0.2%0.3%0.3%Jul 26Sep 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-48998 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 395,492 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected
🐘guzzlehttp/psr7

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

Description

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:

  1. An attacker controls a raw HTTP request or server variable containing a Host value.
  2. The Host value contains URI authority delimiters, such as [email protected].
  3. guzzlehttp/psr7 uses that value to construct a URI.
  4. The URI parser treats the portion before @ as userinfo and the portion after @ as the URI host.
  5. 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\parse_request() 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 parse_request(), 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

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐘Packagistguzzlehttp/psr7all versions2.10.2composer require guzzlehttp/psr7:^2.10.2

Affected Products

1 product · 1 configurations
Application
psr-7guzzlephp
< 2.10.2
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for guzzlehttp/psr7, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update guzzlehttp/psr7 to 2.10.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-48998 is resolved across your whole dependency graph.

  3. Workarounds

    Restrict outbound requests from the affected component to an allowlist of hosts, block access to link-local and internal address ranges at the network layer, and require authentication on internal services so a forged request cannot reach them unauthenticated.

Frequently Asked Questions

## 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: 1. An attacker controls a raw HTTP request or server variable containing a `Host` value. 2. The `Host` value contains URI authority delimiters, such as `[email protected]`. 3. `guzzlehttp/psr7` uses that va
O3 Security · Impact-Aware SCA

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CVE-2026-48998: psr7 — Fixed in 2.10.2