VulnerabilityPublished 10 Nov 2026

CVE-2026-125110: Rack::Static header_rules bypass via dot-segment normalization mismatch

Affects rackSource GCVE Database

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Authoritative record:CVE-2026-125110· Medium 5.3

Not known to be exploited · CVSS 5.3 Medium : upgrade to 2.2.25 when convenient.

Data as of 10 Nov 2026, 19:06 UTC

CVSS 3.1 base score

5.3Medium

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

Thin evidence

One scorer or none

CVSS scores by source
CNA (GitHub_M)	CVSS 3.1	5.3

Patch: Available – fixed in 2.2.25, 3.1.23, 3.2.8

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

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

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: None: There is no loss of confidentiality within 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: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 9 Nov 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 10 Nov 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 rack to 2.2.25; rack to 3.1.23; rack to 3.2.8.

Affected software

Product	Affected	Fixed in
RubyGemsrack	Affected <2.2.25	Fixed in 2.2.25
RubyGemsrack	Affected >=3.0.0 <3.1.23	Fixed in 3.1.23
RubyGemsrack	Affected >=3.2.0 <3.2.8	Fixed in 3.2.8

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

AI-suggested

Update to a patched version of Rack where header_rules are matched against the same normalized path used to serve files (versions 2.2.25, 3.1.23, or 3.2.8 and later). Alternatively, reject requests containing dot segments at a reverse proxy or application boundary. Avoid relying solely on Rack::Static header_rules to prevent inline rendering of untrusted uploads; serve such files from a separate origin.

Description

A path normalization mismatch in Rack::Static header_rules allows bypassing security headers for protected static files. Requests with dot segments can access files without the intended security headers applied, potentially exposing files without Content-Disposition or restrictive Content-Security-Policy headers.

Impact

An unauthenticated attacker who knows the path of a protected static file can bypass security headers such as Content-Disposition or Content-Security-Policy by requesting the file through a dot-segment path. The file content itself is not altered, but the absence of security headers may allow inline rendering of untrusted uploads or other security policy bypasses. Applications not using path-specific header_rules are not affected.

Summary

The Rack::Static middleware normalizes request paths with dot segments when serving files but matches header_rules against only URL-decoded paths without dot-segment normalization. This discrepancy allows attackers to request protected static files via dot-segment paths (e.g., /assets/../uploads/file.html) and receive the file without the security headers configured for its actual location. The issue persists even in versions that fixed a related CVE by adding URL decoding to rule matching but not dot-segment normalization. This affects applications using header_rules to attach security-relevant headers to specific paths or file types.

CWE-180Incorrect Behavior Order: Validate Before Canonicalize (opens in a new tab)
Variant weakness
The product validates input before it is canonicalized.
Implementation · Input Validation
Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174).
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (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
Leverage Alternate Encoding (opens in a new tab)
Using Leading 'Ghost' Character Sequences to Bypass Input Filters (opens in a new tab)
Using Unicode Encoding to Bypass Validation Logic (opens in a new tab)
Using Escaped Slashes in Alternate Encoding (opens in a new tab)
Using Slashes in Alternate Encoding (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 10 Nov 2026, 19:06 UTC

WeaknessesCWE-180

Technical details

References

Community reviews

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