Moderate severityNVD Advisory· Published Jun 17, 2024· Updated Nov 3, 2025
Proxy-Authorization request header isn't stripped during cross-origin redirects in urllib3
CVE-2024-37891
Description
urllib3 is a user-friendly HTTP client library for Python. 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 header, but we still decided to strip the header by default in order to further protect users who aren't using the correct approach. We believe the number of usages affected by this advisory is low. It requires all of the following to be true to be exploited: 1. Setting the Proxy-Authorization header without using urllib3's built-in proxy support. 2. Not disabling HTTP redirects. 3. Either not using an HTTPS origin server or for the proxy or target origin to redirect to a malicious origin. Users are advised to update to either version 1.26.19 or version 2.2.2. Users unable to upgrade may use the Proxy-Authorization header with urllib3's ProxyManager, disable HTTP redirects using redirects=False when sending requests, or not user the Proxy-Authorization header as mitigations.
Affected packages
Versions sourced from the GitHub Security Advisory.
| Package | Affected versions | Patched versions |
|---|---|---|
urllib3PyPI | < 1.26.19 | 1.26.19 |
urllib3PyPI | >= 2.0.0, < 2.2.2 | 2.2.2 |
Affected products
1Patches
240b6d1605814Merge pull request from GHSA-34jh-p97f-mpxf
5 files changed · +41 −6
CHANGES.rst+5 −0 modified@@ -1,6 +1,11 @@ Changes ======= +1.26.19 (2024-06-17) +================== + +- Added the ``Proxy-Authorization`` header to the list of headers to strip from requests when redirecting to a different host. As before, different headers can be set via ``Retry.remove_headers_on_redirect``. + 1.26.18 (2023-10-17) --------------------
src/urllib3/util/retry.py+3 −1 modified@@ -235,7 +235,9 @@ class Retry(object): RETRY_AFTER_STATUS_CODES = frozenset([413, 429, 503]) #: Default headers to be used for ``remove_headers_on_redirect`` - DEFAULT_REMOVE_HEADERS_ON_REDIRECT = frozenset(["Cookie", "Authorization"]) + DEFAULT_REMOVE_HEADERS_ON_REDIRECT = frozenset( + ["Cookie", "Authorization", "Proxy-Authorization"] + ) #: Maximum backoff time. DEFAULT_BACKOFF_MAX = 120
test/test_retry_deprecated.py+5 −1 modified@@ -295,7 +295,11 @@ def test_retry_method_not_in_whitelist(self): def test_retry_default_remove_headers_on_redirect(self): retry = Retry() - assert retry.remove_headers_on_redirect == {"authorization", "cookie"} + assert retry.remove_headers_on_redirect == { + "authorization", + "proxy-authorization", + "cookie", + } def test_retry_set_remove_headers_on_redirect(self): retry = Retry(remove_headers_on_redirect=["X-API-Secret"])
test/test_retry.py+5 −1 modified@@ -293,7 +293,11 @@ def test_retry_method_not_in_whitelist(self): def test_retry_default_remove_headers_on_redirect(self): retry = Retry() - assert retry.remove_headers_on_redirect == {"authorization", "cookie"} + assert retry.remove_headers_on_redirect == { + "authorization", + "proxy-authorization", + "cookie", + } def test_retry_set_remove_headers_on_redirect(self): retry = Retry(remove_headers_on_redirect=["X-API-Secret"])
test/with_dummyserver/test_poolmanager.py+23 −3 modified@@ -142,21 +142,30 @@ def test_redirect_cross_host_remove_headers(self): "GET", "%s/redirect" % self.base_url, fields={"target": "%s/headers" % self.base_url_alt}, - headers={"Authorization": "foo", "Cookie": "foo=bar"}, + headers={ + "Authorization": "foo", + "Proxy-Authorization": "bar", + "Cookie": "foo=bar", + }, ) assert r.status == 200 data = json.loads(r.data.decode("utf-8")) assert "Authorization" not in data + assert "Proxy-Authorization" not in data assert "Cookie" not in data r = http.request( "GET", "%s/redirect" % self.base_url, fields={"target": "%s/headers" % self.base_url_alt}, - headers={"authorization": "foo", "cookie": "foo=bar"}, + headers={ + "authorization": "foo", + "proxy-authorization": "baz", + "cookie": "foo=bar", + }, ) assert r.status == 200 @@ -165,6 +174,8 @@ def test_redirect_cross_host_remove_headers(self): assert "authorization" not in data assert "Authorization" not in data + assert "proxy-authorization" not in data + assert "Proxy-Authorization" not in data assert "cookie" not in data assert "Cookie" not in data @@ -174,7 +185,11 @@ def test_redirect_cross_host_no_remove_headers(self): "GET", "%s/redirect" % self.base_url, fields={"target": "%s/headers" % self.base_url_alt}, - headers={"Authorization": "foo", "Cookie": "foo=bar"}, + headers={ + "Authorization": "foo", + "Proxy-Authorization": "bar", + "Cookie": "foo=bar", + }, retries=Retry(remove_headers_on_redirect=[]), ) @@ -183,6 +198,7 @@ def test_redirect_cross_host_no_remove_headers(self): data = json.loads(r.data.decode("utf-8")) assert data["Authorization"] == "foo" + assert data["Proxy-Authorization"] == "bar" assert data["Cookie"] == "foo=bar" def test_redirect_cross_host_set_removed_headers(self): @@ -194,6 +210,7 @@ def test_redirect_cross_host_set_removed_headers(self): headers={ "X-API-Secret": "foo", "Authorization": "bar", + "Proxy-Authorization": "baz", "Cookie": "foo=bar", }, retries=Retry(remove_headers_on_redirect=["X-API-Secret"]), @@ -205,6 +222,7 @@ def test_redirect_cross_host_set_removed_headers(self): assert "X-API-Secret" not in data assert data["Authorization"] == "bar" + assert data["Proxy-Authorization"] == "baz" assert data["Cookie"] == "foo=bar" r = http.request( @@ -213,6 +231,7 @@ def test_redirect_cross_host_set_removed_headers(self): fields={"target": "%s/headers" % self.base_url_alt}, headers={ "x-api-secret": "foo", + "proxy-authorization": "baz", "authorization": "bar", "cookie": "foo=bar", }, @@ -226,6 +245,7 @@ def test_redirect_cross_host_set_removed_headers(self): assert "x-api-secret" not in data assert "X-API-Secret" not in data assert data["Authorization"] == "bar" + assert data["Proxy-Authorization"] == "baz" assert data["Cookie"] == "foo=bar" def test_redirect_without_preload_releases_connection(self):
accff72ecc2fMerge pull request from GHSA-34jh-p97f-mpxf
4 files changed · +37 −5
CHANGES.rst+5 −0 modified@@ -1,3 +1,8 @@ +2.2.2 (2024-06-17) +================== + +- Added the ``Proxy-Authorization`` header to the list of headers to strip from requests when redirecting to a different host. As before, different headers can be set via ``Retry.remove_headers_on_redirect``. + 2.2.1 (2024-02-16) ==================
src/urllib3/util/retry.py+3 −1 modified@@ -189,7 +189,9 @@ class Retry: RETRY_AFTER_STATUS_CODES = frozenset([413, 429, 503]) #: Default headers to be used for ``remove_headers_on_redirect`` - DEFAULT_REMOVE_HEADERS_ON_REDIRECT = frozenset(["Cookie", "Authorization"]) + DEFAULT_REMOVE_HEADERS_ON_REDIRECT = frozenset( + ["Cookie", "Authorization", "Proxy-Authorization"] + ) #: Default maximum backoff time. DEFAULT_BACKOFF_MAX = 120
test/test_retry.py+5 −1 modified@@ -334,7 +334,11 @@ def test_retry_method_not_allowed(self) -> None: def test_retry_default_remove_headers_on_redirect(self) -> None: retry = Retry() - assert retry.remove_headers_on_redirect == {"authorization", "cookie"} + assert retry.remove_headers_on_redirect == { + "authorization", + "proxy-authorization", + "cookie", + } def test_retry_set_remove_headers_on_redirect(self) -> None: retry = Retry(remove_headers_on_redirect=["X-API-Secret"])
test/with_dummyserver/test_poolmanager.py+24 −3 modified@@ -144,21 +144,30 @@ def test_redirect_cross_host_remove_headers(self) -> None: "GET", f"{self.base_url}/redirect", fields={"target": f"{self.base_url_alt}/headers"}, - headers={"Authorization": "foo", "Cookie": "foo=bar"}, + headers={ + "Authorization": "foo", + "Proxy-Authorization": "bar", + "Cookie": "foo=bar", + }, ) assert r.status == 200 data = r.json() assert "Authorization" not in data + assert "Proxy-Authorization" not in data assert "Cookie" not in data r = http.request( "GET", f"{self.base_url}/redirect", fields={"target": f"{self.base_url_alt}/headers"}, - headers={"authorization": "foo", "cookie": "foo=bar"}, + headers={ + "authorization": "foo", + "proxy-authorization": "baz", + "cookie": "foo=bar", + }, ) assert r.status == 200 @@ -167,6 +176,8 @@ def test_redirect_cross_host_remove_headers(self) -> None: assert "authorization" not in data assert "Authorization" not in data + assert "proxy-authorization" not in data + assert "Proxy-Authorization" not in data assert "cookie" not in data assert "Cookie" not in data @@ -176,7 +187,11 @@ def test_redirect_cross_host_no_remove_headers(self) -> None: "GET", f"{self.base_url}/redirect", fields={"target": f"{self.base_url_alt}/headers"}, - headers={"Authorization": "foo", "Cookie": "foo=bar"}, + headers={ + "Authorization": "foo", + "Proxy-Authorization": "bar", + "Cookie": "foo=bar", + }, retries=Retry(remove_headers_on_redirect=[]), ) @@ -185,6 +200,7 @@ def test_redirect_cross_host_no_remove_headers(self) -> None: data = r.json() assert data["Authorization"] == "foo" + assert data["Proxy-Authorization"] == "bar" assert data["Cookie"] == "foo=bar" def test_redirect_cross_host_set_removed_headers(self) -> None: @@ -196,6 +212,7 @@ def test_redirect_cross_host_set_removed_headers(self) -> None: headers={ "X-API-Secret": "foo", "Authorization": "bar", + "Proxy-Authorization": "baz", "Cookie": "foo=bar", }, retries=Retry(remove_headers_on_redirect=["X-API-Secret"]), @@ -207,11 +224,13 @@ def test_redirect_cross_host_set_removed_headers(self) -> None: assert "X-API-Secret" not in data assert data["Authorization"] == "bar" + assert data["Proxy-Authorization"] == "baz" assert data["Cookie"] == "foo=bar" headers = { "x-api-secret": "foo", "authorization": "bar", + "proxy-authorization": "baz", "cookie": "foo=bar", } r = http.request( @@ -229,12 +248,14 @@ def test_redirect_cross_host_set_removed_headers(self) -> None: assert "x-api-secret" not in data assert "X-API-Secret" not in data assert data["Authorization"] == "bar" + assert data["Proxy-Authorization"] == "baz" assert data["Cookie"] == "foo=bar" # Ensure the header argument itself is not modified in-place. assert headers == { "x-api-secret": "foo", "authorization": "bar", + "proxy-authorization": "baz", "cookie": "foo=bar", }
Vulnerability mechanics
Generated by null/stub on May 9, 2026. Inputs: CWE entries + fix-commit diffs from this CVE's patches. Citations validated against bundle.
References
8- github.com/advisories/GHSA-34jh-p97f-mpxfghsaADVISORY
- nvd.nist.gov/vuln/detail/CVE-2024-37891ghsaADVISORY
- github.com/urllib3/urllib3/commit/40b6d1605814dd1db0a46e202d6e56f2e4c9a468ghsaWEB
- github.com/urllib3/urllib3/commit/accff72ecc2f6cf5a76d9570198a93ac7c90270eghsax_refsource_MISCWEB
- github.com/urllib3/urllib3/security/advisories/GHSA-34jh-p97f-mpxfghsax_refsource_CONFIRMWEB
- lists.debian.org/debian-lts-announce/2024/12/msg00020.htmlghsaWEB
- security.netapp.com/advisory/ntap-20240822-0003ghsaWEB
- www.vicarius.io/vsociety/posts/proxy-authorization-header-handling-vulnerability-in-urllib3-cve-2024-37891ghsaWEB
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