How severe is CVE-2026-9658?

CVE-2026-9658 has a CVSS 3.x base score of 7.3, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability low.

Is CVE-2026-9658 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (13th percentile), an estimate of the probability of exploitation in the next 30 days.

How do I fix CVE-2026-9658?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-9658 have an EU (EUVD) identifier?

Yes. CVE-2026-9658 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-32892.

When was CVE-2026-9658 published?

CVE-2026-9658 was published on 2026-05-28 and last updated on 2026-06-17.

CVE-2026-9658

CVE-2026-9658 is a high-severity vulnerability with a CVSS 3.x base score of 7.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-113.

Key facts

Severity: High (CVSS 3.x base score 7.3)
EPSS exploit prediction: 0% (13th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-32892
Weakness: CWE-113
Published: 2026-05-28
Last modified: 2026-06-17

Description

Plack::Middleware::Security::Common versions before 0.13.1 for Perl did not block header injections in request paths. The header injection rule was ineffective at blocking header injections in the request paths unless they were double-encoded, for example, GET /path\r\nHTTP/1.1\r\nHost: secret.example.com Note that it is unclear whether request paths with CRLF followed by additional headers would be blocked by reverse proxies, or how they would be processed by Plack-based servers.

Frequently asked questions

What is CVE-2026-9658?: Plack::Middleware::Security::Common versions before 0.13.1 for Perl did not block header injections in request paths. The header injection rule was ineffective at blocking header injections in the request paths unless they were double-encoded, for example, GET /path\r\nHTTP/1.1\r\nHost: secret.example.com Note that it is unclear whether request paths with CRLF followed by additional headers would be blocked by reverse proxies, or how they would be processed by Plack-based servers.
How severe is CVE-2026-9658?: CVE-2026-9658 has a CVSS 3.x base score of 7.3, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability low.
Is CVE-2026-9658 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (13th percentile), an estimate of the probability of exploitation in the next 30 days.
How do I fix CVE-2026-9658?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-9658 have an EU (EUVD) identifier?: Yes. CVE-2026-9658 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-32892.
When was CVE-2026-9658 published?: CVE-2026-9658 was published on 2026-05-28 and last updated on 2026-06-17.

References

Other CWE-113 (HTTP Response Splitting) vulnerabilities

CVE-2026-38967 — Critical (CVSS 9.8): CrowCpp Crow through v1.3.1 HTTP is vulnerable to response header injection via unvalidated response header values.
CVE-2026-34520 — Critical (CVSS 9.1): AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.13.4, the C parser…
CVE-2025-53007 — High (CVSS 8.9): arduino-esp32 provides an Arduino core for the ESP32. Versions prior to 3.3.0-RC1 and 3.2.1 contain a HTTP Response…
CVE-2024-52875 — High (CVSS 8.8): An issue was discovered in GFI Kerio Control 9.2.5 through 9.4.5. The dest GET parameter passed to the…
CVE-2018-0689 — High (CVSS 8.8): HTTP header injection vulnerability in SEIKO EPSON printers and scanners (DS-570W firmware versions released prior to…
CVE-2018-11347 — High (CVSS 8.8): The YunoHost 2.7.2 through 2.7.14 web application is affected by one HTTP Response Header Injection. This flaw allows…

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