VulnerabilityPublished 10 Nov 2026

CVE-2026-126080: Possible DoS vulnerability in Active Support safe_constantize

Affects activesupportSource GCVE Database

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Authoritative record:CVE-2026-126080· High 7.5

Not known to be exploited · CVSS 7.5 High : upgrade to 8.1.4.1 soon.

Data as of 10 Nov 2026, 22:34 UTC

CVSS 3.1 base score

7.5High

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	7.5

Patch: Available – fixed in 8.1.4.1, 8.0.5.2

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

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

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: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 10 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 activesupport to 8.1.4.1; activesupport to 8.0.5.2.

Affected software

Product	Affected	Fixed in
RubyGemsactivesupport	Affected >=8.1.0.beta1 <8.1.4.1	Fixed in 8.1.4.1
RubyGemsactivesupport	Affected <8.0.5.2	Fixed in 8.0.5.2

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

Description

### Impact When constant lookup raises `LoadError`, `ActiveSupport::Inflector#safe_constantize` (and `String#safe_constantize`) builds a regular expression from the requested constant name without escaping it, so a caller that passes untrusted input lets the attacker choose the source of a pattern that the application compiles. Crafted patterns can trigger defects in Ruby's regular expression compiler, possibly leading to a crash of the server process, and repeated requests could keep the application unavailable. Action Cable passes the `channel` value of each `subscribe` command to `safe_constantize` before any channel lookup, so in the default configuration an unauthenticated client of the Action Cable endpoint can reach this code. ### Details The check that decides whether `safe_constantize` returns `nil` or re-raises the `LoadError` now matches the first segment of the constant name against the error message as a literal string, and no longer compiles a regular expression. It returns the same result as before for constant names that contain no regular expression syntax. ### Affected applications An application is affected if it meets all of these requirements: - Mounts Action Cable, which a new Rails application does by default at `/cable` (`config.action_cable.mount_path`), or otherwise passes untrusted input to `safe_constantize`. - Accepts Action Cable connections from untrusted clients. `ApplicationCable::Connection#connect` authenticates nobody unless the application adds a check. ### Workarounds Applications that do not use Action Cable can set `config.action_cable.mount_path = nil` to remove the endpoint. Applications that use Action Cable can call `reject_unauthorized_connection` in `ApplicationCable::Connection#connect` for unauthenticated clients, which limits exposure to authenticated users but does not remove it. ### Releases The fixed releases are available at the normal locations. Patches for those who cannot upgrade at once: - 8.1: https://github.com/rails/rails/commit/95aa9e416016524956d4904fed96eaed079580bb.patch - 8.0: https://github.com/rails/rails/commit/210ac22d446c8e2625b091e79256806b836eee20.patch ### Versions affected - activesupport < 8.0.5.2 - activesupport >= 8.1, < 8.1.4.1 ### Credit This issue was responsibly reported by Felix Tscheulin ([flixt](https://hackerone.com/flixt)) through HackerOne researcher [scheja](https://hackerone.com/scheja), and independently by Bucky Wolfe ([Igneous](https://github.com/Igneous)), who provided a proof of concept that crashes the server. It was also found by the Anthropic OSS Scanner (ANT-2026-ZUN5KU3Q).

CWE-74Improper Neutralization of Special Elements in Output Used by a Downstream Component (Injection) (opens in a new tab)
Class weaknessLikelihood of exploit: HighOWASP Top 10 A05:2025: Injection (opens in a new tab)
The product constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component.
MITRE discourages mapping vulnerabilities to this broad entry; the root cause is usually a more specific weakness.
Requirements
Programming languages and supporting technologies might be chosen which are not subject to these issues.
Implementation
Utilize an appropriate mix of allowlist and denylist parsing to filter control-plane syntax from all input.
OWASP Cheat Sheets
Abuse Case (opens in a new tab)
Deserialization (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
V1.5.1 (opens in a new tab)
Attack patterns
Buffer Overflow via Environment Variables (opens in a new tab)
Server Side Include (SSI) Injection (opens in a new tab)
HTTP Request Splitting (opens in a new tab)
Command Line Execution through SQL Injection (opens in a new tab)
Double Encoding (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

WeaknessesCWE-74

Technical details

References

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