KEVWire

Security intelligence, with context.

Response snapshot Nov 3, 2026, 19:21 UTC

Back to the wire
Permalink
VulnerabilityCVE-2026-44266

Elo Ruby backend has Remote Code Execution via unescaped `#{...}` interpolation in emitted string literals and subtype-constraint labels

Elo's Ruby backend emits attacker-controlled text into Ruby double-quoted strings without escaping the # character. Because # begins Ruby's interpolation sequences — #{expr}, #@ivar, #@@cvar, #$gvar — and any expression wrapped in #{...

Published Updated

At a glance

Exploited
Not known
Severity
9.8 Critical (CVSS 3.1)
Chance of exploitation
Not estimated
Sources
2 independent sources

What to do

GitHub lists first patched versions: @enspirit/elo: 1.0.1. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-7w38-ggh5-v542 (opens a new tab)

What happened

Summary

Elo's Ruby backend emits attacker-controlled text into Ruby double-quoted strings without escaping the # character. Because # begins Ruby's interpolation sequences — #{expr}, #@ivar, #@@cvar, #$gvar — and any expression wrapped in #{...

} may use backticks for shell execution, an Elo program that contains a crafted string literal or a labelled subtype constraint compiles to Ruby that evaluates attacker-chosen Ruby, and through backticks runs attacker-chosen shell commands, at runtime.

The same Elo source compiled to JavaScript, Python, or SQL is benign, so the bug also breaks the cross-target portability guarantee the rest of the compiler honours.

Continue reading

Vulnerable sinks

Two sinks exist in src/compilers/ruby.ts at commit 749af7b:

1. String-literal emitter — lines 180–184. The emitter escapes backslash, double quote, and control characters, but not #. Any #{...} sequence in an Elo string literal flows straight into the emitted Ruby source.

2. Labelled subtype-constraint branch — lines 405–412. The error message passed to p_fail(p, "...") is wrapped in a Ruby double-quoted string with no escape pass at all. Because the parser at src/parser.ts:1339–1348 accepts single-quoted Elo strings as constraint labels, a label such as '#{ ` id }'` flows unchanged into the emitted Ruby.

Attack surfaces

All three surfaces share the same root cause (the missing # escape in the Ruby double-quoted-string emission path) and are addressed by the same patch:

| # | Entry point | Threat model | |---|---|---| | 1 | /try playground on elo-lang.org (Ruby target) | 0-click server-side RCE against elo-lang.org infrastructure from a shared PoC URL | | 2 | bin/eloc -t ruby -x on a CI or DevOps host | RCE on any host that passes Elo strings through the CLI | | 3 | Library API — defaultFormats.elo.

parse() with a Ruby emission step | Ruby RCE for any downstream integrator using Elo as a rule engine, configuration DSL, or form builder DSL (the primary documented use cases) |

Proof of Concept

String-literal sink:

# poc.elo
'RES=#{`id 2>&1`}'
$ eloc -t ruby -x poc.elo
# emitted Ruby contains: "RES=#{`id 2>&1`}"
# running it returns the output of id(1).

Replacing ` id 2>&1 with touch /tmp/pwned ` produces a trivially observable filesystem side effect.

Subtype-constraint label sink:

# poc-subtype.elo
let X = Int(i | '#{`touch /tmp/pwned2`}': i > 0) in X(-1)

The predicate fails for -1, causing p_fail(p, "#{...}") to interpolate and execute the backtick command at the Ruby layer.

Both flows are automated in the reproduction script submitted with the original report and were verified against Ruby 3.x.

Root cause

The Ruby-emitter's double-quoted-string escape routine omitted # from its character set, and one emission path (the subtype-constraint label branch) performed no escape pass at all.

Affected package ranges reported by GitHub: @enspirit/elo: <= 1.0.0

Scores and how they were measured

CVSS base severity

9.8

Version 3.1As of

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

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

Not available

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Follow JavaScript packages (npm): RSS feedAll its recordsAsk your AI assistant

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-7w38-ggh5-v542 (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-7w38-ggh5-v542, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    NVD CVE-2026-44266 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  4. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  5. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, November 3). Elo Ruby backend has Remote Code Execution via unescaped `#{...}` interpolation in emitted string literals and subtype-constraint labels (CVE-2026-44266). https://kevwire.com/record/CVE-2026-44266

MLA

"Elo Ruby backend has Remote Code Execution via unescaped `#{...}` interpolation in emitted string literals and subtype-constraint labels (CVE-2026-44266)." KEVWire, 3 Nov. 2026, kevwire.com/record/CVE-2026-44266.

Chicago

KEVWire. "Elo Ruby backend has Remote Code Execution via unescaped `#{...}` interpolation in emitted string literals and subtype-constraint labels (CVE-2026-44266)." Last modified November 3, 2026. https://kevwire.com/record/CVE-2026-44266.

Evidence summary (plain text)

Elo Ruby backend has Remote Code Execution via unescaped `#{...}` interpolation in emitted string literals and subtype-constraint labels (Nov 3, 2026).
Elo's Ruby backend emits attacker-controlled text into Ruby double-quoted strings without escaping the # character. Because # begins Ruby's interpolation sequences — #{expr}, #@ivar, #@@cvar, #$gvar — and any expression wrapped in #{...} may use backticks for shell execution, an Elo program that contains a crafted string literal or a labelled subtype constraint compiles to Ruby that evaluates attacker-chosen Ruby, and through backticks runs attacker-chosen shell commands, at runtime.
CVSS 9.8 (version 3.1; evidence as of Nov 3, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-44266).
Sources:
GitHub-reviewed advisory GHSA-7w38-ggh5-v542: https://github.com/advisories/GHSA-7w38-ggh5-v542
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
NVD CVE-2026-44266: https://nvd.nist.gov/vuln/detail/CVE-2026-44266
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-11-03T17:35:57.416Z&lastModEndDate=2026-11-03T19:05:57.748Z&resultsPerPage=500&startIndex=0
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-11-03T17:01:00.112Z&lastModEndDate=2026-11-03T18:35:55.788Z&resultsPerPage=500&startIndex=0
Record ID: CVE-2026-44266.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Nov 3, 2026, 19:05 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

Record JSON

Your account

Email alerts

Email alerts are coming as part of KEVWire Premium: join the waitlist. To follow your stack today, use its RSS feed, which honors your filters, or connect an AI agent through the API.

Suggest an improvement

Ideas, missing sources, corrections, and bugs are all welcome. No account needed. Suggestions are reviewed by a person before anything changes.

Record details

Record detail