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fkie_cve-2026-97687

urllib3 is an HTTP client library for Python. From 1.26.0 until 2.8.0, the proxy_ssl_context, proxy_assert_hostname, proxy_assert_fingerprint, ssl_context, cert_reqs, verify_mode, use_forwarding_for_https=True, and CERT_NONE configuration paths fail to remain separated because target-server TLS settings are incorrectly applied to the HTTPS proxy connection. The trigger is that an application uses an HTTPS proxy and configures target-server TLS settings that must remain separate from the proxy TLS handshake, including HTTPS forwarding with target-specific identity or credentials. Applying cert_reqs=CERT_NONE can overwrite proxy_ssl_context.verify_mode in place, and the mutation persists so later connections reusing the same context may connect to the HTTPS proxy without certificate verification. The attack mechanism is that an attacker intercepts and impersonates the HTTPS proxy after the effective proxy policy accepts the attacker's certificate. The impact is that the attacker can observe or modify forwarded traffic or receive a target TLS client certificate, while CONNECT tunneling still preserves the separate end-to-end target TLS connection. This issue is fixed in version 2.8.0.

GHSA-8988-9cw3-xx77 — urllib3: HTTPS proxy TLS configuration may be ignored or overridden

Affected: PyPI: urllib3

## Impact

urllib3 supports configuring TLS independently for an HTTPS proxy and the target server.

`proxy_ssl_context`, `proxy_assert_hostname`, and `proxy_assert_fingerprint` configure the TLS connection to the proxy. `ssl_context` 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 `proxy_ssl_context` 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 `cert_reqs="CERT_NONE"` for a target server could overwrite the `verify_mode` of the SSL context configured for the HTTPS proxy. This modification occurred in place and persisted on the context object, potentially disabling proxy certificate verification for later connections that reused the same context.

An attacker able to intercept the connection to an HTTPS proxy may be able to impersonate the proxy when the effective proxy TLS configuration disables certificate verification or otherwise accepts the attacker's certificate. This may occur, for example, when the target server's trust…

RHSA-2026:69612 — Red Hat Security Advisory: Red Hat Hardened Images RPMs bug fix and enhancement update

urllib3: urllib3: Traffic interception via HTTPS proxy TLS configuration override urllib3: urllib3: Denial of Service via infinite loop during chunked Deflate decoding urllib3: urllib3: Denial of Service via unbounded memory allocation in chunk parser