CVE-2026-3783 — token leak with redirect and netrc

Affected: curl

When an OAuth2 bearer token is used for an HTTP(S) transfer, and that transfer performs a redirect to a second URL, curl could leak that token to the second hostname under some circumstances.

If the hostname that the first request is redirected to has information in the used .netrc file, with either of the `machine` or `default` keywords, curl would pass on the bearer token set for the first host also to the second one.

USN-8084-1 — curl vulnerabilities

Affected: Ubuntu:22.04:LTS: curl, Ubuntu:24.04:LTS: curl, Ubuntu:25.10: curl

Zhicheng Chen discovered that curl could incorrectly reuse the wrong connection for Negotiate-authenticated HTTP or HTTPS requests. This could result in the use of credentials from a different connection, contrary to expectations. (CVE-2026-1965)

It was discovered that curl incorrectly leaked OAuth2 bearer tokens when following a redirect. This could result in tokens being sent to the wrong host, contrary to expectations. (CVE-2026-3783)

Muhamad Arga Reksapati discovered that curl incorrectly reused existing HTTP proxy connections even if the request used different credentials. This could result in the use of incorrect credentials, contrary to expectations. (CVE-2026-3784)

Daniel Wade discovered that curl incorrectly handled certain memory operations when doing a second SMB request to the same host. An attacker could use this issue to cause curl to crash, resulting in a denial of service, or possibly execute arbitrary code. This issue only affected Ubuntu 25.10. (CVE-2026-3805)

Yihang Zhou discovered that curl incorrectly reused .netrc file credentials when following redirects. This could result in the use of credentials for a different host, contrary to expectations. This issue only affected Ubuntu 22.04 LTS and Ubuntu 24.04 LTS. (CVE-2025-0167)

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CVE-2026-3783 — token leak with redirect and netrc

USN-8084-1 — curl vulnerabilities