KEVWire

Security intelligence, with context.

Response snapshot Oct 31, 2026, 01:26 UTC

Back to the wire
Permalink
VulnerabilityCVE-2026-54442

NationalSecurityAgency/emissary has an incomplete fix for CVE-2026-35571

The URL validation regex ^(https?:/)?/.* added to emissary's NavAction.java allows protocol-relative URLs (//evil.com/...) and single-slash scheme variants (http:/evil.com) to bypass validation, enabling SSRF and open redirect attacks.

At a glance

Exploited
Not known
Severity
4.8 Medium (CVSS 3.1)
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: gov.nsa.emissary:emissary: 8.51.0. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-c6q7-wqw2-h65w (opens a new tab)

What happened

Summary

The URL validation regex ^(https?:/)?/.* added to emissary's NavAction.java allows protocol-relative URLs (//evil.com/...) and single-slash scheme variants (http:/evil.com) to bypass validation, enabling SSRF and open redirect attacks.

Affected Package

- Ecosystem: Maven - Package: NationalSecurityAgency/emissary - Affected versions: = e2078417464b

Continue reading

Severity

Medium

CWE

CWE-918 — Server-Side Request Forgery (SSRF)

Details

The fix in NavAction.java (line 47) introduces a VALID_LINK pattern:

Pattern.compile("^(https?:/)?/.*")

This regex is intended to restrict navigation links to relative paths and HTTP/HTTPS URLs. However, it has multiple bypass vectors.

Protocol-relative URLs (//evil.com/...): The group (https?:/)? is optional, so the pattern reduces to //.* when the group is absent. This matches //evil.com/steal?c=SESSION, which browsers resolve to the current page's protocol plus the attacker's host.

Single-slash scheme (http:/evil.com): The regex group captures http:/ as a valid match, and browsers normalize http:/evil.com to http://evil.com, creating an open redirect to the attacker's server.

Protocol-relative to cloud metadata (//169.254.169.254/...): This enables SSRF to cloud instance metadata endpoints, which is particularly dangerous in AWS/GCP environments where IAM credentials can be retrieved.

The pre-fix code had no validation at all, accepting any URL. The fix blocks javascript:, ftp:, and data: URIs, but the protocol-relative and single-slash bypasses remain exploitable.

PoC

"""
CVE-2026-35571 - NationalSecurityAgency/emissary SSRF via NavAction

The fix in commit e2078417464b adds URL scheme validation using:
 Pattern.compile("^(https?:/)?/.*")

This allows protocol-relative URLs (//evil.com) and single-slash variants
(http:/evil.com) to bypass the validation.

Tested against: emissary@0d4dc56 (pre-fix) and patch e207841
Extracted from: src/main/java/emissary/server/mvc/NavAction.java:47
"""

import re
import sys

FIXED_PATTERN = re.compile(r"^(https?:/)?/.*")

def vulnerable_accepts(link: str) -> bool:
 """Pre-fix behaviour: no validation, everything passes."""
 return True

def fixed_accepts(link: str) -> bool:
 """Post-fix behaviour: must match VALID_LINK pattern."""
 return bool(FIXED_PATTERN.match(link))

TEST_VECTORS = [
 ("javascript: XSS payload",
 "javascript:alert(document.cookie)", True),
 ("ftp: scheme",
 "ftp://evil.com/exfil", True),
 ("data: URI",
 "data:text/html,", True),

 ("Relative path",
 "/path/to/resource", False),
 ("HTTP URL",
 "http://trusted.internal:8080/api", False),
 ("HTTPS URL",
 "https://trusted.internal/api", False),

 ("Protocol-relative URL to attacker host (//evil.com)",
 "//evil.com/steal?c=SESSION", True),
 ("Protocol-relative with embedded credentials",
 "//user:pass@evil.com/path", True),
 ("Protocol-relative to cloud metadata (//169.254.169.254)",
 "//169.254.169.254/latest/meta-data/", True),
 ("Backslash trick (\\\\evil.com)",
 "\\\\evil.com/path", True),
 ("Tab in scheme (java\\tscript:...)",
 "java\tscript:alert(1)", True),
 ("Path starting with attacker-like host (/evil.com)",
 "/evil.com", False),
 ("Triple slash (///evil.com)",
 "///evil.com/etc/passwd", True),
 ("http:/ single-slash to attacker host",
 "http:/evil.com/steal", True),
 ("https:/ single-slash to attacker host",
 "https:/evil.com/steal", True),
 ("URL-encoded javascript scheme (%6a...)",
 "%6aavascript:alert(1)", True),
 ("CRLF injection in path",
 "/legit\r\nLocation: http://evil.com", True),
]

def main():
 print("=" * 72)
 print("CVE-2026-35571 -- Emissary NavAction SSRF / Open-Redirect PoC")
 print("Pattern under test: ^(https?:/)?/.*")
 print("=" * 72)
 print()

 bypasses_found = []
 results_table = []

 for desc, url, should_block in TEST_VECTORS:
 vuln_result = vulnerable_accepts(url)
 fixed_result = fixed_accepts(url)

 if should_block and fixed_result:
 status = "BYPASS"
 bypasses_found.append((desc, url))
 elif should_block and not fixed_result:
 status = "BLOCKED (good)"
 elif not should_block and fixed_result:
 status = "ALLOWED (good)"
 elif not should_block and not fixed_result:
 status = "FALSE-POS"
 else:
 status = "UNKNOWN"

 results_table.append((desc, url, vuln_result, fixed_result, status))

 for desc, url, vuln, fixed, status in results_table:
 display_url = repr(url) if len(url) > 50 else url
 print(f"[{status:>15}] {desc}")
 print(f"{'':>17} URL: {display_url}")
 print(f"{'':>17} pre-fix={vuln} post-fix={fixed}")
 print()

 print("=" * 72)
 print(f"Total vectors tested : {len(TEST_VECTORS)}")
 print(f"Bypasses found : {len(bypasses_found)}")
 print()

 if bypasses_found:
 print("VULNERABILITY CONFIRMED -- the following vectors bypass the fix:")
 print()
 for desc, url in bypasses_found:
 print(f" - {desc}")
 print(f" URL: {repr(url)}")
 print()
 print("Key finding: The regex ^(https?:/)?/.* allows protocol-relative")
 print("URLs (//evil.com/...) because the optional group (https?:/) can be")
 print("absent, leaving //.* which matches //attacker.com. This enables")
 print("SSRF to arbitrary external hosts via navigation links.")
 print()
 print("Additionally, http:/evil.com and https:/evil.com match the regex")
 print("(group 1 captures 'http:/' or 'https:/') and browsers normalise")
 print("these to http://evil.com, enabling open redirect / SSRF.")
 sys.exit(0)
 else:
 print("No bypasses found -- fix appears complete.")
 sys.exit(1)

if __name__ == "__main__":
 main()

Steps to reproduce: 1. Run python3 poc.py 2. Observe that protocol-relative and single-slash URLs bypass the regex

Expected output:

VULNERABILITY CONFIRMED
Protocol-relative URLs (//evil.com/) and single-slash variants (http:/evil.com) bypass the regex validation.

Impact

An attacker can craft navigation links that bypass URL validation to redirect users to attacker-controlled servers (open redirect) or make the emissary server

Affected package ranges reported by GitHub: gov.nsa.emissary:emissary: < 8.51.0

Scores and how they were measured

CVSS base severity

4.8

Version 3.1As of

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

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

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-c6q7-wqw2-h65w (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-c6q7-wqw2-h65w, its actual identifiers, source dates, and structured metrics.

    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, October 30). NationalSecurityAgency/emissary has an incomplete fix for CVE-2026-35571 (CVE-2026-54442). https://kevwire.com/record/CVE-2026-54442

MLA

"NationalSecurityAgency/emissary has an incomplete fix for CVE-2026-35571 (CVE-2026-54442)." KEVWire, 30 Oct. 2026, kevwire.com/record/CVE-2026-54442.

Chicago

KEVWire. "NationalSecurityAgency/emissary has an incomplete fix for CVE-2026-35571 (CVE-2026-54442)." Last modified October 30, 2026. https://kevwire.com/record/CVE-2026-54442.

Evidence summary (plain text)

NationalSecurityAgency/emissary has an incomplete fix for CVE-2026-35571 (Oct 30, 2026).
The URL validation regex ^(https?:/)?/.* added to emissary's NavAction.java allows protocol-relative URLs (//evil.com/...) and single-slash scheme variants (http:/evil.com) to bypass validation, enabling SSRF and open redirect attacks.

- Ecosystem: Maven
- Package: NationalSecurityAgency/emissary
- Affected versions: = e2078417464b

Medium

CWE-918 — Server-Side Request Forgery (SSRF)

The fix in NavAction.java (line 47) introduces a VALID_LINK pattern:

This regex is intended to restrict navigation links to relative paths and HTTP/HTTPS URLs. However, it has multiple bypass vectors.
CVSS 4.8 (version 3.1; evidence as of Oct 30, 2026; https://github.com/advisories/GHSA-c6q7-wqw2-h65w).
Sources:
GitHub-reviewed advisory GHSA-c6q7-wqw2-h65w: https://github.com/advisories/GHSA-c6q7-wqw2-h65w
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
Record ID: CVE-2026-54442.
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: Oct 31, 2026, 00:50 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