GHSA-48p4-8xcf-vxj5 CVE-2025-50182 PYSEC-2026-1997

urllib3 does not control redirects in browsers and Node.js

Medium PyPI

Severity: 5.3 / 10; Medium · CVSS 3.1
Exploit chance (EPSS): 0.60%; Chance of exploitation in the next 30 days. Higher than 48.79% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-601 URL Redirection to Untrusted Site ('Open Redirect')
Fix: 2.5.0; Upgrade urllib3 to this version or later

Description

urllib3 supports being used in a Pyodide runtime utilizing the JavaScript Fetch API or falling back on XMLHttpRequest. This means you can use Python libraries to make HTTP requests from your browser or Node.js. Additionally, urllib3 provides a mechanism to control redirects.

However, the retries and redirect parameters are ignored with Pyodide; the runtime itself determines redirect behavior.

Affected usages

Any code which relies on urllib3 to control the number of redirects for an HTTP request in a Pyodide runtime.

Impact

Redirects are often used to exploit SSRF vulnerabilities. An application attempting to mitigate SSRF or open redirect vulnerabilities by disabling redirects may remain vulnerable if a Pyodide runtime redirect mechanism is unsuitable.

Remediation

If you use urllib3 in Node.js, upgrade to a patched version of urllib3.

Unfortunately, browsers provide no suitable way which urllib3 can use: XMLHttpRequest provides no control over redirects, the Fetch API returns opaqueredirect responses lacking data when redirects are controlled manually. Expect default browser behavior for redirects.

Affected versions

PyPI

Package	Vulnerable	Fixed in
urllib3	`>= 2.2.0, < 2.5.0`	`2.5.0`
urllib3	`>= 2.2.0, < 2.5.0`	`2.5.0`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

urllib3 PyPI → `2.5.0`

pip

pip install --upgrade "urllib3>=2.5.0"

poetry

poetry add "urllib3>=2.5.0"

uv

uv add "urllib3>=2.5.0"

Severity breakdown

CVSS 3.1 5.3

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

Attack vector: Network
Attack complexity: High
Privileges required: Low
User interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: None
Availability: None

Weakness

CWE-601: URL Redirection to Untrusted Site ('Open Redirect')

The web application accepts a user-controlled input that specifies a link to an external site, and uses that link in a redirect.

How to prevent it

Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright. Use a list of approved URLs or domains to be used for redirection.
Architecture and Design: Use an intermediate disclaimer page that provides the user with a clear warning that they are leaving the current site. Implement a long timeout before the redirect occurs, or force the user to click on the link. Be careful to avoid XSS problems (CWE-79) when generating the disclaimer page.
Architecture and Design: When the set of acceptable objects, such as filenames or URLs, is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames or URLs, and reject all other inputs. For example, ID 1 could map to "/login.asp" and ID 2 could map to "http://www.example.com/". Features such as the ESAPI AccessReferenceMap [REF-45] provide this capability.
Architecture and Design: Ensure that no externally-supplied requests are honored by requiring that all redirect requests include a unique nonce generated by the application [REF-483]. Be sure that the nonce is not predictable (CWE-330).
Architecture and Design, Implementation: Understand all the potential areas where untrusted inputs can enter your software: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls. Many open redirect problems occur because the programmer assumed that certain inputs could not be modified, such as cookies and hidden form fields.
Operation: Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth [REF-1481].

References

Advisories

Fixes and patches

github.com/urllib3/urllib3/commit/7eb4a2aafe49a279c29b6d1f0ed0f42e9736194f

Packages

Timeline

Jun 18, 2025 Published
Sep 10, 2026 Last updated by the source
Nov 1, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-vxq7-64xx-v4gw urllib3: HTTPResponse.stream()/read_chunked() buffers an unbounded chunk-size line into memory	High	Also affects urllib3
GHSA-gh4c-6fx4-qh6g urllib3: Chunked Deflate streaming can enter an infinite loop	Medium	Also affects urllib3
GHSA-8988-9cw3-xx77 urllib3: HTTPS proxy TLS configuration may be ignored or overridden	High	Also affects urllib3
GHSA-mf9v-mfxr-j63j urllib3: Decompression-bomb safeguards bypassed in parts of the streaming API	High	Also affects urllib3
GHSA-qccp-gfcp-xxvc urllib3: Sensitive headers forwarded across origins in proxied low-level redirects	High	Also affects urllib3
GHSA-38jv-5279-wg99 Decompression-bomb safeguards bypassed when following HTTP redirects (streaming API)	High	Also affects urllib3
GHSA-2xpw-w6gg-jr37 urllib3 streaming API improperly handles highly compressed data	High	Also affects urllib3
GHSA-gm62-xv2j-4w53 urllib3 allows an unbounded number of links in the decompression chain	High	Also affects urllib3

Credits: illia-v, pquentin, sethmlarson

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