Koajs vulnerable to Cross-Site Scripting (XSS) at ctx.redirect() function

Description

Summary

In koa < 2.16.1 and < 3.0.0-alpha.5, passing untrusted user input to ctx.redirect() even after sanitizing it, may execute javascript code on the user who use the app.

Patches

This issue is patched in 2.16.1 and 3.0.0-alpha.5.

PoC

Coming soon...

Impact

  1. Redirect user to another phishing site
  2. Make request to another endpoint of the application based on user's cookie
  3. Steal user's cookie

Basic information

Type
reviewed
Severity
medium
Advisory on GitHub
Open advisory ↗
Repository advisory
Open repository advisory ↗
Source code
Browse source ↗
Published (advisory)
2025-04-09 13:00:07 UTC
Updated
2025-10-05 07:09:57 UTC
GitHub reviewed
2025-04-09 13:00:07 UTC
NVD published
2025-04-09

EPSS Score

Score Percentile
0.18% 40.11%

CVSS Scores

Base score Version Severity Vector
5.0 3.1
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:L Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:L)
Might cause slowdowns, glitches, or partial disruption—not a full brick.

Identifiers

CWEs

CWE id Name
CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Affected packages (2)

Vulnerable version ranges and first patched releases as published by GitHub.

Ecosystem Package Vulnerable range First patched Vulnerable functions
npm koa < 2.16.1 2.16.1
npm koa >= 3.0.0-alpha.1, < 3.0.0-alpha.5 3.0.0-alpha.5

References

cvelogic Threat Intelligence