Analyst readout for executives and security teams
Plain-English summary
CVE-2026-12209 affects RubyLouvre avalon’s template filter handling. A remote attacker may be able to modify JavaScript object prototypes, which can undermine application logic and potentially lead to code injection impacts. Public exploit material is referenced, but active exploitation is not confirmed by KEV or the provided sources.
Executive priority
Treat as a timely remediation review for applications using avalon, not as a confirmed breach event. Public exploit availability raises urgency, but current evidence does not confirm active exploitation or a vendor patch. Prioritize internet-facing or high-trust applications that process user-controlled template data.
Technical view
The issue is reported in src/filters/index.js within avalon Template Filter Handler. VulDB describes improperly controlled modification of object prototype attributes, with CWE-1321 and CWE-94 assigned. CVSS v4.0 is 6.9, network-accessible, low complexity, no privileges, and no user interaction. Affected versions are reported at least through 2.2.10, with source inconsistency on the lower bound.
Likely exposure
Exposure is most likely in applications that directly include RubyLouvre avalon versions listed as affected, especially where untrusted data can influence template filters. The provided data lists 2.2.0 through 2.2.10; one VulDB submission also references 0.9.9 through 2.2.10.
Exploitation context
The vulnerability is remotely reachable and exploit material is publicly referenced, including a GitHub repository. However, the bundle does not show CISA KEV inclusion or another cited source confirming active exploitation. Vendor contact reportedly received no response, and no official fix is identified in the provided sources.
Researcher notes
Evidence is incomplete and partly inconsistent. The CVE bundle lists affected versions 2.2.0 through 2.2.10, while a VulDB submission title references 0.9.9 through 2.2.10. No vendor response or official remediation is cited. Avoid assuming broader products or confirmed exploitation beyond the referenced public disclosure.
Mitigation direction
- Inventory applications using RubyLouvre avalon and record exact versions.
- Prioritize review of versions 2.2.0 through 2.2.10.
- Check RubyLouvre or package repository guidance for any fixed release.
- If no fix exists, evaluate removing or replacing avalon where feasible.
- Restrict untrusted input from reaching avalon template filter logic.
- Monitor VulDB, CVE, and project repositories for updates.
Validation and detection
- Search dependency manifests and bundled JavaScript for avalon usage.
- Confirm deployed avalon versions against affected ranges in CVE and VulDB.
- Review whether template filters process user-controlled input.
- Check application logs for unusual template rendering errors or prototype pollution indicators.
- Track whether any official vendor advisory or patched version appears.
Public sources used
Based on public source material and reviewed before publication.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-1321: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCWE-94: Code execution behavior lookup
Code execution and unsafe deserialization weaknesses often justify reviewing execution behavior and process telemetry. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2026-12209 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 6.9 (4.0)
- Known Exploited
- No
- Published
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
4 official scoresWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P — — VulDB CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N/E:P/RL:X/RC:R 3.9 1.4 VulDB CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N/E:P/RL:X/RC:R 3.9 1.4 VulDB AV:N/AC:L/Au:N/C:N/I:P/A:N/E:POC/RL:ND/RC:UR 10 2.9 VulDB Vulnerability scoring details
Base CVSS 4.0 score
6.9 MediumVector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P
Base CVSS 3.1 score
5.3 MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N/E:P/RL:X/RC:R
Base CVSS 3.0 score
5.3 MediumVector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N/E:P/RL:X/RC:R
Base CVSS 2.0 score
5 MediumVector: AV:N/AC:L/Au:N/C:N/I:P/A:N/E:POC/RL:ND/RC:UR
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- Source timeline VulDB
Advisory disclosed
- Source timeline VulDB
VulDB entry created
- CVE reserved CVE Program
The CVE ID was reserved by the assigning CNA.
- Source timeline VulDB
VulDB entry last update
- CVE published CVE Program
The CVE record was published.
- CVE updated CVE Program
The CVE record metadata indicates this as the latest update time.
Source materials
- CVE List V5 source CVE List V5
- VDB-370851 | RubyLouvre avalon Template Filter index.js prototype pollution CVE reference, VulDB · vdb-entry
- VDB-370851 | CTI Indicators (IOB, IOC, TTP, IOA) CVE reference, VulDB · signature, permissions-required
- CVE-2026-12209 | CVE Analysis and Report CVE reference, VulDB · third-party-advisory
- Submit #832447 | RubyLouvre avalon 0.9.9 - 2.2.10 Code Injection / Prototype Pollution CVE reference, VulDB · third-party-advisory
- https://github.com/OriginSecurityX/avalon-filter-rce CVE reference, VulDB · exploit
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.
Improper Control of Generation of Code ('Code Injection')
Improper Control of Generation of Code ('Code Injection') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.