VulnerabilityPublished 28 May 2026Updated 1 Jun 2026

CVE-2026-9658: RRWO Plack::Middleware::Security::Common · Improper Filtering of Special Elements

Affects RRWO Plack::Middleware::Security::CommonSource CVE Database V5

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Not known to be exploited · CVSS 7.3 High : upgrade to 0.13.1 soon.

Data as of 29 Oct 2026, 19:04 UTC

CVSS 3.1 base score

7.3High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.2% chance of exploitation in 30 days – higher than 13% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 0.13.1

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: Low
Integrity: Low
Availability: Low

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 28 May 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade Plack::Middleware::Security::Common and Plack-Middleware-Security-Simple to 0.13.1.

Affected software

Product	Affected	Fixed in
RRWOPlack::Middleware::Security::Common	Affected <0.13.1	Fixed in 0.13.1
GitHubPlack-Middleware-Security-Simple`pkg:github/Plack-Middleware-Security-Simple`Other threats	Affected <0.13.1	Fixed in 0.13.1

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

In the meantime, consider implementing additional input validation or filtering at the application or proxy level to detect and block CRLF injection attempts in request paths.

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.

Impact

The vulnerability allows an attacker to perform HTTP header injection via request paths, potentially leading to response splitting or manipulation of HTTP headers. This can result in information disclosure, cache poisoning, or other injection-based attacks depending on how the injected headers are handled by servers or proxies. The CVSS score of 7.3 reflects a high severity with network attack vector, no privileges or user interaction required, and impacts on confidentiality, integrity, and availability. However, the actual impact depends on the environment and how intermediaries process the injected headers.

Summary

Plack::Middleware::Security::Common versions prior to 0.13.1 fail to properly filter special elements in request paths, specifically CRLF sequences that enable header injection attacks. The header injection rule is ineffective unless the injection is double-encoded, allowing attackers to insert malicious headers into HTTP requests. This vulnerability is categorized under CWE-790 (Improper Filtering of Special Elements) and CWE-113 (Improper Neutralization of CRLF Sequences). The exact behavior of downstream components like reverse proxies or Plack servers when processing such injected headers is not clearly defined, which may affect the exploitability and impact.

CWE-790Improper Filtering of Special Elements (opens in a new tab)
Class weakness
The product receives data from an upstream component, but it does not filter or incorrectly filters special elements before sending it to a downstream component.
OWASP Cheat Sheets
Abuse Case (opens in a new tab)
Deserialization (opens in a new tab)
Server Side Request Forgery Prevention (opens in a new tab)
Unvalidated Redirects and Forwards (opens in a new tab)
Cross Site Scripting Prevention (opens in a new tab)
OWASP ASVS 4.0.3
V1.5.1 (opens in a new tab)
V5.2.2 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-113Improper Neutralization of CRLF Sequences in HTTP Headers (HTTP Request Splitting) (opens in a new tab)
Variant weaknessOWASP Top 10 A05:2025: Injection (opens in a new tab)
The product receives data from an HTTP agent/component (e.g., web server, proxy, browser, etc.), but it does not neutralize or incorrectly neutralizes CR and LF characters before the data is included in outgoing HTTP headers.
Implementation · Input Validation
Construct HTTP headers very carefully, avoiding the use of non-validated input data.
Implementation · Input Validation
Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. If an input does not strictly conform to specifications, reject it or transform it into something that conforms.
Implementation · Output Encoding
Use and specify an output encoding that can be handled by the downstream component that is reading the output. Common encodings include ISO-8859-1, UTF-7, and UTF-8.
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
Injection Prevention (opens in a new tab)
SQL Injection Prevention (opens in a new tab)
Injection Prevention in Java (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
V5.1.3 (opens in a new tab)
Attack patterns
HTTP Request Splitting (opens in a new tab)
Accessing/Intercepting/Modifying HTTP Cookies (opens in a new tab)
HTTP Response Splitting (opens in a new tab)
AJAX Footprinting (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 4 Jun 2026, 20:40 UTC

WeaknessesCWE-790, CWE-113

Technical details

References

Community reviews

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