CVE-2025-62595
Description
A flaw was found in Koa. A bypass of CVE-2025-8129 was discovered in the Koa.js framework affecting its back redirect functionality. In certain circumstances, an attacker can manipulate the Referer header to force a user’s browser to navigate to an external, potentially malicious website. This occurs because the implementation incorrectly treats some specially crafted URLs as safe relative paths. This issue allows attackers to perform phishing, social engineering, or other redirect-based attacks on users of affected applications.
Statement
To exploit this flaw, an attacker needs to convince a user into visiting a malicious link, limiting the possibility of exploitation. However, this vulnerability still has a moderate severity due to the impact of redirect-based attacks.
Mitigation
Applications can use the following workarounds to mitigate this vulnerability:
Do not treat //host as a safe relative path. Explicitly exclude protocol‑relative values from any relative‑path branch.
Normalize the Referer by resolving it with a base (e.g., new URL(rawRef, ctx.href)), then compare resolved.origin (scheme+host+port) to ctx.origin (or ctx.host plus scheme/port) before allowing the redirect.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 4.3 | 6.1 | N/A |
| Attack Vector | Network | Network | N/A |
| Attack Complexity | Low | Low | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | Required | Required | N/A |
| Scope | Unchanged | Changed | N/A |
| Confidentiality | None | Low | N/A |
| Integrity Impact | Low | Low | N/A |
| Availability Impact | None | None | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Understanding the Weakness (CWE)
Access Control
Technical Impact: Bypass Protection Mechanism; Gain Privileges or Assume Identity
The user may be redirected to an untrusted page that contains malware which may then compromise the user's system. In some cases, an open redirect can also enable the immediate download of a file without the user's permission, because the redirection to an external site may lead to endpoints on those sites that automatically trigger a download action ("drive-by download" [REF-1478]). This will expose the user to extensive risk. The user's interaction with the web server may also be compromised if the malware conducts keylogging or other attacks that steal credentials, personally identifiable information (PII), or other important data.
Access Control,Confidentiality,Other
Technical Impact: Bypass Protection Mechanism; Gain Privileges or Assume Identity; Other
By modifying the URL value to a malicious site, an attacker may successfully launch a phishing scam. The user may be subjected to phishing attacks by being redirected to an untrusted page. The phishing attack may point to an attacker controlled web page that appears to be a trusted web site. The phishers may then steal the user's credentials and then use these credentials to access the legitimate web site. Because the server name in the modified link is identical to the original site, phishing attempts have a more trustworthy appearance.
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