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22 actionable advisories, newest first. Withdrawn advisories and news are excluded. Coverage is partial.
Impact urllib3's streaming API is designed for the efficient handling of large HTTP responses by reading content in chunks instead of loading the entire response body into memory at once. urllib3 can decompress response bodies according to the HTTP Content-Encoding header. When streaming a compressed, chunked response, urllib3 first consumes data already buffered by the decoder before reading the next HTTP chunk. However, urllib3 versions from 2.6.2 through 2.7.0 could enter an infinite loop when a chunked response contained bytes after the end of the Deflate stream. If the decompressed body exceeded the requested streaming chunk size, Python's zlib implementation could retain the trailing bytes as unconsumed input after reaching the end of the compressed stream. urllib3 would repeatedly attempt to decode those same bytes without making progress or reading more data from the network. A malicious server could exploit this behavior to cause excessive CPU usage and prevent the affected…
Recommended action: Upgrade to 2.8.0 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.
Impact urllib3's streaming API is designed for efficiently handling large HTTP responses by reading the content in chunks, rather than loading the entire response body into memory at once. When decoding a chunked-transfer-encoded response, this API reads each chunk's size field by buffering until it sees \n or EOF. A malicious HTTP server can return Transfer-Encoding: chunked and then send a very long run of bytes without any newline, causing the streaming client to buffer that entire run before urllib3 can reject the chunk size as invalid and allocate more memory than intended. To fix the issue, we'll reject chunk-size fields larger than 65536 bytes, as already done in the non-streaming case, which is currently handled by the Python standard library. Note that this only applies to reading the chunk-size field, not the chunk data, which is already handled correctly. Thus, there shouldn't be any impact for non-malicious servers. Affected usages Applications and libraries using urllib3…
Recommended action: Upgrade to 2.8.0 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.
Impact urllib3 supports configuring TLS independently for an HTTPS proxy and the target server. proxysslcontext, proxyasserthostname, and proxyassertfingerprint configure the TLS connection to the proxy. sslcontext and the other target-specific TLS parameters configure the connection to the target server. In urllib3 versions 1.26.0 through 2.7.0, these configurations were not consistently separated. Depending on the proxy mode, urllib3 could: 1. Ignore proxysslcontext and use the target server's SSL context for the TLS connection to an HTTPS forwarding proxy. 2. Override the HTTPS proxy's certificate-verification policy with the target server's certificate-verification policy. 3. Apply target-specific SNI, hostname assertions, certificate fingerprint assertions, or TLS client credentials to the TLS connection to an HTTPS forwarding proxy. In particular, configuring certreqs="CERTNONE" for a target server could overwrite the verifymode of the SSL context configured for the HTTPS…
Recommended action: Upgrade to 2.8.0 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.
Impact urllib3's streaming API is designed for the efficient handling of large HTTP responses by reading the content in chunks, rather than loading the entire response body into memory at once. urllib3 can perform decompression based on the HTTP Content-Encoding header (e.g., gzip, deflate, br, or zstd). When using the streaming API since version 2.6.0, the library decompresses only the necessary bytes, enabling partial content consumption. However, urllib3 before version 2.7.0 could still decompress the whole response instead of the requested portion in two cases: 1. During the second HTTPResponse.read(amt=N) call when the response was decompressed using the official Brotli library. 2. When HTTPResponse.drainconn() was called after the response had been read and decompressed partially (compression algorithm did not matter here). These issues could cause urllib3 to fully decode a small amount of highly compressed data in a single operation. This could result in excessive resource…
Recommended action: Upgrade to 2.7.0 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.
Impact When following cross-origin redirects for requests made using urllib3’s high-level APIs, such as urllib3.request(), PoolManager.request(), and ProxyManager.request(), sensitive headers — Authorization, Cookie, and Proxy-Authorization (defined in Retry.DEFAULTREMOVEHEADERSONREDIRECT) — are stripped by default, as expected. However, cross-origin redirects followed from the low-level API via ProxyManager.connectionfromurl().urlopen(..., assertsamehost=False) still forward these sensitive headers. Affected usage Applications and libraries using urllib3 versions earlier than 2.7.0 may be affected if they allow cross-origin redirects while making requests through HTTPConnection.urlopen() instances created via ProxyManager.connectionfromurl(). Remediation Upgrade to urllib3 version 2.7.0 or later, in which sensitive headers are stripped from redirects followed by HTTPConnection. If upgrading is not immediately possible, avoid using this low-level redirect flow for cross-origin…
Recommended action: Upgrade to 2.7.0 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.
Impact urllib3's streaming API is designed for the efficient handling of large HTTP responses by reading the content in chunks, rather than loading the entire response body into memory at once. urllib3 can perform decoding or decompression based on the HTTP Content-Encoding header (e.g., gzip, deflate, br, or zstd). When using the streaming API, the library decompresses only the necessary bytes, enabling partial content consumption. However, for HTTP redirect responses, the library would read the entire response body to drain the connection and decompress the content unnecessarily. This decompression occurred even before any read methods were called, and configured read limits did not restrict the amount of decompressed data. As a result, there was no safeguard against decompression bombs. A malicious server could exploit this to trigger excessive resource consumption on the client (high CPU usage and large memory allocations for decompressed data; CWE-409). Affected usages…
Recommended action: Upgrade to 2.6.3 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.
Impact urllib3's streaming API is designed for the efficient handling of large HTTP responses by reading the content in chunks, rather than loading the entire response body into memory at once. When streaming a compressed response, urllib3 can perform decoding or decompression based on the HTTP Content-Encoding header (e.g., gzip, deflate, br, or zstd). The library must read compressed data from the network and decompress it until the requested chunk size is met. Any resulting decompressed data that exceeds the requested amount is held in an internal buffer for the next read operation. The decompression logic could cause urllib3 to fully decode a small amount of highly compressed data in a single operation. This can result in excessive resource consumption (high CPU usage and massive memory allocation for the decompressed data; CWE-409) on the client side, even if the application only requested a small chunk of data. Affected usages Applications and libraries using urllib3 version…
Recommended action: Upgrade to 2.6.0 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.
Impact urllib3 supports chained HTTP encoding algorithms for response content according to RFC 9110 (e.g., Content-Encoding: gzip, zstd). However, the number of links in the decompression chain was unbounded allowing a malicious server to insert a virtually unlimited number of compression steps leading to high CPU usage and massive memory allocation for the decompressed data. Affected usages Applications and libraries using urllib3 version 2.5.0 and earlier for HTTP requests to untrusted sources unless they disable content decoding explicitly. Remediation Upgrade to at least urllib3 v2.6.0 in which the library limits the number of links to 5. If upgrading is not immediately possible, use preloadcontent=False and ensure that resp.headers["content-encoding"] contains a safe number of encodings before reading the response content.
Recommended action: Upgrade to 2.6.0 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.
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…
Recommended action: Upgrade to 2.5.0 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.
urllib3 handles redirects and retries using the same mechanism, which is controlled by the Retry object. The most common way to disable redirects is at the request level, as follows: However, it is also possible to disable redirects, for all requests, by instantiating a PoolManager and specifying retries in a way that disable redirects: However, the retries parameter is currently ignored, which means all the above examples don't disable redirects. Affected usages Passing retries on PoolManager instantiation to disable redirects or restrict their number. By default, requests and botocore users are not affected. Impact Redirects are often used to exploit SSRF vulnerabilities. An application attempting to mitigate SSRF or open redirect vulnerabilities by disabling redirects at the PoolManager level will remain vulnerable. Remediation You can remediate this vulnerability with the following steps: Upgrade to a patched version of urllib3. If your organization would benefit from the…
Recommended action: Upgrade to 2.5.0 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.
When using urllib3's proxy support with ProxyManager, the Proxy-Authorization header is only sent to the configured proxy, as expected. However, when sending HTTP requests without using urllib3's proxy support, it's possible to accidentally configure the Proxy-Authorization header even though it won't have any effect as the request is not using a forwarding proxy or a tunneling proxy. In those cases, urllib3 doesn't treat the Proxy-Authorization HTTP header as one carrying authentication material and thus doesn't strip the header on cross-origin redirects. Because this is a highly unlikely scenario, we believe the severity of this vulnerability is low for almost all users. Out of an abundance of caution urllib3 will automatically strip the Proxy-Authorization header during cross-origin redirects to avoid the small chance that users are doing this on accident. Users should use urllib3's proxy support or disable automatic redirects to achieve safe processing of the Proxy-Authorization…
Recommended action: Upgrade to 2.2.2 or 1.26.19 by release line, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.
urllib3 previously wouldn't remove the HTTP request body when an HTTP redirect response using status 303 "See Other" after the request had its method changed from one that could accept a request body (like POST) to GET as is required by HTTP RFCs. Although the behavior of removing the request body is not specified in the section for redirects, it can be inferred by piecing together information from different sections and we have observed the behavior in other major HTTP client implementations like curl and web browsers. From RFC 9110 Section 9.3.1: A client SHOULD NOT generate content in a GET request unless it is made directly to an origin server that has previously indicated, in or out of band, that such a request has a purpose and will be adequately supported. Affected usages Because the vulnerability requires a previously trusted service to become compromised in order to have an impact on confidentiality we believe the exploitability of this vulnerability is low. Additionally,…
Recommended action: Upgrade to 2.0.7 or 1.26.18 by release line, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.
urllib3 before 1.24.2 does not remove the authorization HTTP header when following a cross-origin redirect (i.e., a redirect that differs in host, port, or scheme). This can allow for credentials in the authorization header to be exposed to unintended hosts or transmitted in cleartext. NOTE: this issue exists because of an incomplete fix for CVE-2018-20060 (which was case-sensitive).
Recommended action: Upgrade to 1.24.2 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.
urllib3 doesn't treat the Cookie HTTP header special or provide any helpers for managing cookies over HTTP, that is the responsibility of the user. However, it is possible for a user to specify a Cookie header and unknowingly leak information via HTTP redirects to a different origin if that user doesn't disable redirects explicitly. Users must handle redirects themselves instead of relying on urllib3's automatic redirects to achieve safe processing of the Cookie header, thus we decided to strip the header by default in order to further protect users who aren't using the correct approach. Affected usages We believe the number of usages affected by this advisory is low. It requires all of the following to be true to be exploited: Using an affected version of urllib3 (patched in v1.26.17 and v2.0.6) Using the Cookie header on requests, which is mostly typical for impersonating a browser. Not disabling HTTP redirects Either not using HTTPS or for the origin server to redirect to a…
Recommended action: Upgrade to 2.0.6 or 1.26.17 by release line, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.
Versions 1.17 and 1.18 of the Python urllib3 library suffer from a vulnerability that can cause them, in certain configurations, to not correctly validate TLS certificates. This places users of the library with those configurations at risk of man-in-the-middle and information leakage attacks. This vulnerability affects users using versions 1.17 and 1.18 of the urllib3 library, who are using the optional PyOpenSSL support for TLS instead of the regular standard library TLS backend, and who are using OpenSSL 1.1.0 via PyOpenSSL. This is an extremely uncommon configuration, so the security impact of this vulnerability is low.
Recommended action: Upgrade to 1.18.1 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.
In the urllib3 library through 1.24.2 for Python, CRLF injection is possible if the attacker controls the request parameter.
Recommended action: Upgrade to 1.24.3 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.
urllib3 before 1.25.9 allows CRLF injection if the attacker controls the HTTP request method, as demonstrated by inserting CR and LF control characters in the first argument of putrequest(). NOTE: this is similar to CVE-2020-26116.
Recommended action: Upgrade to 1.25.9 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.
Impact When provided with a URL containing many @ characters in the authority component the authority regular expression exhibits catastrophic backtracking causing a denial of service if a URL were passed as a parameter or redirected to via an HTTP redirect. Patches The issue has been fixed in urllib3 v1.26.5. References - CVE-2021-33503 - JVNVU#92413403 (English) - JVNVU#92413403 (Japanese) - urllib3 v1.26.5 For more information If you have any questions or comments about this advisory: Ask in our community Discord Email sethmichaellarson@gmail.com
Recommended action: Upgrade to 1.26.5 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.
The encodeinvalidchars function in util/url.py in the urllib3 library 1.25.2 through 1.25.7 for Python allows a denial of service (CPU consumption) because of an inefficient algorithm. The percentencodings array contains all matches of percent encodings. It is not deduplicated. For a URL of length N, the size of percentencodings may be up to O(N). The next step (normalize existing percent-encoded bytes) also takes up to O(N) for each step, so the total time is O(N^2). If percentencodings were deduplicated, the time to compute encodeinvalidchars would be O(kN), where k is at most 484 ((10+62)^2).
Recommended action: Upgrade to 1.25.8 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.
Impact Users who are using an HTTPS proxy to issue HTTPS requests and haven't configured their own SSLContext via proxyconfig. Only the default SSLContext is impacted. Patches urllib3 =1.26.4 has the issue resolved. urllib3<1.26 is not impacted due to not supporting HTTPS requests via HTTPS proxies. Workarounds Upgrading is recommended as this is a minor release and not likely to break current usage. Configuring an SSLContext with checkhostname=True and passing via proxyconfig instead of relying on the default SSLContext For more information If you have any questions or comments about this advisory: Email us at sethmichaellarson@gmail.com
Recommended action: Upgrade to 1.26.4 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.
The urllib3 library before 1.24.2 for Python mishandles certain cases where the desired set of CA certificates is different from the OS store of CA certificates, which results in SSL connections succeeding in situations where a verification failure is the correct outcome. This is related to use of the sslcontext, cacerts, or cacertsdir argument.
Recommended action: Upgrade to 1.24.2 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.
urllib3 before version 1.23 does not remove the Authorization HTTP header when following a cross-origin redirect (i.e., a redirect that differs in host, port, or scheme). This can allow for credentials in the Authorization header to be exposed to unintended hosts or transmitted in cleartext.
Recommended action: Upgrade to 1.23 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.