{"id":"CVE-2021-39155","aliases":["EUVD-2021-1611","GHSA-7774-7vr3-cc8j","RHSA-2021:3272","RHSA-2021:3273"],"status":"published","title":"Authorization Policy Bypass Due to Case Insensitive Host Comparison","description":"Istio is an open source platform for providing a uniform way to integrate microservices, manage traffic flow across microservices, enforce policies and aggregate telemetry data. According to [RFC 4343](https://datatracker.ietf.org/doc/html/rfc4343), Istio authorization policy should compare the hostname in the HTTP Host header in a case insensitive way, but currently the comparison is case sensitive. The proxy will route the request hostname in a case-insensitive way which means the authorization policy could be bypassed. As an example, the user may have an authorization policy that rejects request with hostname \"httpbin.foo\" for some source IPs, but the attacker can bypass this by sending the request with hostname \"Httpbin.Foo\". Patches are available in Istio 1.11.1, Istio 1.10.4 and Istio 1.9.8. As a work around a Lua filter may be written to normalize Host header before the authorization check. This is similar to the Path normalization presented in the [Security Best Practices](https://istio.io/latest/docs/ops/best-practices/security/#case-normalization) guide.","severity":{"version":"3.1","score":8.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:L","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-09","score":0.01242,"percentile":0.69417,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-178","CWE-863"],"published":"2021-08-24T22:25:18Z","modified":"2026-10-20T10:54:52Z","fixes":[{"ecosystem":"Go","package":"istio.io/istio","fixed_in":["1.9.8","1.10.4","1.11.1"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"Go","package":"istio.io/istio","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.9.8"}]}]},{"source":"ghsa","ecosystem":"Go","package":"istio.io/istio","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"1.10.0"},{"fixed":"1.10.4"}]}]},{"source":"ghsa","ecosystem":"Go","package":"istio.io/istio","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"1.11.0"},{"last_affected":"1.11.0"},{"fixed":"1.11.1"}]}],"versions":["1.11.0"]},{"source":"osv","ecosystem":"Go","package":"istio.io/istio","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"1.9.8"}]}]},{"source":"osv","ecosystem":"Go","package":"istio.io/istio","ranges":[{"type":"SEMVER","events":[{"introduced":"1.10.0"},{"fixed":"1.10.4"}]}]},{"source":"osv","ecosystem":"Go","package":"istio.io/istio","ranges":[{"type":"SEMVER","events":[{"introduced":"1.11.0"},{"fixed":"1.11.1"}]}],"versions":["1.11.0"]},{"source":"osv","ecosystem":"Red Hat:service_mesh:2.0::el8","package":"servicemesh-proxy","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0:2.0.7-3.el8"}]}],"bundled":5},{"source":"osv","ecosystem":"Red Hat:service_mesh:2.0::el8","package":"servicemesh","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0:2.0.7-3.el8"}]}],"bundled":5},{"source":"osv","ecosystem":"Red Hat:service_mesh:2.0::el8","package":"servicemesh-istioctl","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0:2.0.7-3.el8"}]}],"bundled":5},{"source":"osv","ecosystem":"Red Hat:service_mesh:2.0::el8","package":"servicemesh-mixc","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0:2.0.7-3.el8"}]}],"bundled":5},{"source":"osv","ecosystem":"Red Hat:service_mesh:2.0::el8","package":"servicemesh-mixs","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0:2.0.7-3.el8"}]}],"bundled":5},{"source":"osv","ecosystem":"Red Hat:service_mesh:2.0::el8","package":"servicemesh-pilot-agent","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0:2.0.7-3.el8"}]}],"bundled":5},{"source":"osv","ecosystem":"Red Hat:service_mesh:2.0::el8","package":"servicemesh-pilot-discovery","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0:2.0.7-3.el8"}]}],"bundled":5},{"source":"osv","ecosystem":"Red Hat:service_mesh:1.1::el8","package":"servicemesh-proxy","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0:1.1.17-2.el8"}]}],"bundled":5},{"source":"osv","ecosystem":"Red Hat:service_mesh:1.1::el8","package":"servicemesh","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0:1.1.17-3.el8"}]}],"bundled":5},{"source":"osv","ecosystem":"Red Hat:service_mesh:1.1::el8","package":"servicemesh-citadel","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0:1.1.17-3.el8"}]}],"bundled":5},{"source":"osv","ecosystem":"Red Hat:service_mesh:1.1::el8","package":"servicemesh-galley","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0:1.1.17-3.el8"}]}],"bundled":5},{"source":"osv","ecosystem":"Red Hat:service_mesh:1.1::el8","package":"servicemesh-istioctl","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0:1.1.17-3.el8"}]}],"bundled":5},{"source":"osv","ecosystem":"Red Hat:service_mesh:1.1::el8","package":"servicemesh-mixc","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0:1.1.17-3.el8"}]}],"bundled":5},{"source":"osv","ecosystem":"Red Hat:service_mesh:1.1::el8","package":"servicemesh-mixs","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0:1.1.17-3.el8"}]}],"bundled":5},{"source":"osv","ecosystem":"Red Hat:service_mesh:1.1::el8","package":"servicemesh-pilot-agent","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0:1.1.17-3.el8"}]}],"bundled":5},{"source":"osv","ecosystem":"Red Hat:service_mesh:1.1::el8","package":"servicemesh-pilot-discovery","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0:1.1.17-3.el8"}]}],"bundled":5},{"source":"osv","ecosystem":"Red Hat:service_mesh:1.1::el8","package":"servicemesh-sidecar-injector","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0:1.1.17-3.el8"}]}],"bundled":5}],"products":[{"vendor":"istio","product":"istio"}],"references":[{"url":"https://github.com/istio/istio/security/advisories/GHSA-7774-7vr3-cc8j","tags":["x_refsource_CONFIRM","x_transferred","Third Party Advisory","advisory","web"]},{"url":"https://datatracker.ietf.org/doc/html/rfc4343","tags":["x_refsource_MISC","x_transferred","Third Party Advisory","advisory","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-39155","tags":["advisory"]},{"url":"https://github.com/istio/istio/commit/084b417a486dbe9b9024d4812877016a484572b1","tags":["web"]},{"url":"https://github.com/istio/istio/commit/76ed51413ddd2a7fa253a368ab20a9cec5fb1cbe","tags":["web"]},{"url":"https://github.com/istio/istio/commit/90b00bdf891e6c770cb3235c14a9b1fda96cc7c5","tags":["web"]},{"url":"https://github.com/advisories/GHSA-7774-7vr3-cc8j"},{"url":"https://github.com/istio/istio","tags":["package"]},{"url":"https://access.redhat.com/errata/RHSA-2021:3272","tags":["advisory"]},{"url":"https://access.redhat.com/security/updates/classification/#important","tags":["article"]},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=1996915","tags":["report"]},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=1996929","tags":["report"]},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=1996933","tags":["report"]},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=1996934","tags":["report"]},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=1996935","tags":["report"]},{"url":"https://security.access.redhat.com/data/csaf/v2/advisories/2021/rhsa-2021_3272.json","tags":["advisory"]},{"url":"https://access.redhat.com/security/cve/CVE-2021-32777","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2021-32777","tags":["advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-32777","tags":["advisory"]},{"url":"https://istio.io/latest/news/security/istio-security-2021-008/","tags":["article"]},{"url":"https://access.redhat.com/security/cve/CVE-2021-32779","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2021-32779","tags":["advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-32779","tags":["advisory"]},{"url":"https://access.redhat.com/security/cve/CVE-2021-32781","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2021-32781","tags":["advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-32781","tags":["advisory"]},{"url":"https://access.redhat.com/security/cve/CVE-2021-39155","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2021-39155","tags":["advisory"]},{"url":"https://access.redhat.com/security/cve/CVE-2021-39156","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2021-39156","tags":["advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-39156","tags":["advisory"]},{"url":"https://access.redhat.com/errata/RHSA-2021:3273","tags":["advisory"]},{"url":"https://security.access.redhat.com/data/csaf/v2/advisories/2021/rhsa-2021_3273.json","tags":["advisory"]}],"sources":{"cve":[{"id":"CVE-2021-39155","title":"Authorization Policy Bypass Due to Case Insensitive Host Comparison","description":"Istio is an open source platform for providing a uniform way to integrate microservices, manage traffic flow across microservices, enforce policies and aggregate telemetry data. According to [RFC 4343](https://datatracker.ietf.org/doc/html/rfc4343), Istio authorization policy should compare the hostname in the HTTP Host header in a case insensitive way, but currently the comparison is case sensitive. The proxy will route the request hostname in a case-insensitive way which means the authorization policy could be bypassed. As an example, the user may have an authorization policy that rejects request with hostname \"httpbin.foo\" for some source IPs, but the attacker can bypass this by sending the request with hostname \"Httpbin.Foo\". Patches are available in Istio 1.11.1, Istio 1.10.4 and Istio 1.9.8. As a work around a Lua filter may be written to normalize Host header before the authorization check. This is similar to the Path normalization presented in the [Security Best Practices](https://istio.io/latest/docs/ops/best-practices/security/#case-normalization) guide.","status":"published","published":"2021-08-24T22:25:18Z","modified":"2024-08-04T01:58:18.14Z","cvss":[{"version":"3.1","score":8.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:L","level":"high","assessor":"cna"}],"cwes":["CWE-178"],"updated_at":"2026-11-02T14:33:09.540052Z"}],"euvd":[{"id":"EUVD-2021-1611","description":"Istio is an open source platform for providing a uniform way to integrate microservices, manage traffic flow across microservices, enforce policies and aggregate telemetry data. According to [RFC 4343](https://datatracker.ietf.org/doc/html/rfc4343), Istio authorization policy should compare the hostname in the HTTP Host header in a case insensitive way, but currently the comparison is case sensitive. The proxy will route the request hostname in a case-insensitive way which means the authorization policy could be bypassed. As an example, the user may have an authorization policy that rejects request with hostname \"httpbin.foo\" for some source IPs, but the attacker can bypass this by sending the request with hostname \"Httpbin.Foo\". Patches are available in Istio 1.11.1, Istio 1.10.4 and Istio 1.9.8. As a work around a Lua filter may be written to normalize Host header before the authorization check. This is similar to the Path normalization presented in the [Security Best Practices](https://istio.io/latest/docs/ops/best-practices/security/#case-normalization) guide.","status":"published","published":"2021-08-24T22:25:18Z","modified":"2024-08-04T01:58:18Z","cvss":[{"version":"3.1","score":8.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:L","level":"high"}],"updated_at":"2026-11-03T03:24:24.305495Z"}],"ghsa":[{"id":"GHSA-7774-7vr3-cc8j","title":"Authorization Policy Bypass Due to Case Insensitive Host Comparison","description":"### Impact\nAccording to [RFC 4343](https://datatracker.ietf.org/doc/html/rfc4343), Istio authorization policy should compare the hostname in the HTTP Host header in a case insensitive way, but currently the comparison is case sensitive.  The Envoy proxy will route the request hostname in a case-insensitive way which means the authorization policy could be bypassed.\n \nAs an example, the user may have an authorization policy that rejects request with hostname \"httpbin.foo\" for some source IPs, but the attacker can bypass this by sending the request with hostname \"Httpbin.Foo\".\n\n### Patches\n* Istio 1.11.1 and above\n* Istio 1.10.4 and above\n* Istio 1.9.8 and above\n\n### Workarounds\nA Lua filter may be written to normalize Host header before the authorization check.  This is similar to the Path normalization presented in the [Security Best Practices](https://istio.io/latest/docs/ops/best-practices/security/#case-normalization) guide.\n\n### References\nMore details can be found in the [Istio Security Bulletin](https://istio.io/latest/news/security/istio-security-2021-008).\n\n### For more information\nIf you have any questions or comments about this advisory, please email us at istio-security-vulnerability-reports@googlegroups.com\n","status":"published","published":"2021-08-30T16:15:56Z","modified":"2023-05-22T18:26:48Z","cvss":[{"version":"3.1","score":8.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:L","level":"high"}],"cwes":["CWE-178"],"updated_at":"2026-11-02T14:36:53.103029Z"}],"nvd":[{"id":"CVE-2021-39155","description":"Istio is an open source platform for providing a uniform way to integrate microservices, manage traffic flow across microservices, enforce policies and aggregate telemetry data. According to [RFC 4343](https://datatracker.ietf.org/doc/html/rfc4343), Istio authorization policy should compare the hostname in the HTTP Host header in a case insensitive way, but currently the comparison is case sensitive. The proxy will route the request hostname in a case-insensitive way which means the authorization policy could be bypassed. As an example, the user may have an authorization policy that rejects request with hostname \"httpbin.foo\" for some source IPs, but the attacker can bypass this by sending the request with hostname \"Httpbin.Foo\". Patches are available in Istio 1.11.1, Istio 1.10.4 and Istio 1.9.8. As a work around a Lua filter may be written to normalize Host header before the authorization check. This is similar to the Path normalization presented in the [Security Best Practices](https://istio.io/latest/docs/ops/best-practices/security/#case-normalization) guide.","status":"published","published":"2021-08-24T23:15:07.093Z","modified":"2026-06-17T04:03:12.617Z","cvss":[{"version":"3.1","score":8.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:L","level":"high","assessor":"secondary"},{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","level":"high","assessor":"primary"},{"version":"2.0","score":5,"vector":"AV:N/AC:L/Au:N/C:P/I:N/A:N","level":"medium","assessor":"primary"}],"cwes":["CWE-178","CWE-863"],"updated_at":"2026-11-02T14:06:57.67549Z"}],"osv":[{"id":"CVE-2021-39155","description":"Istio is an open source platform for providing a uniform way to integrate microservices, manage traffic flow across microservices, enforce policies and aggregate telemetry data. According to [RFC 4343](https://datatracker.ietf.org/doc/html/rfc4343), Istio authorization policy should compare the hostname in the HTTP Host header in a case insensitive way, but currently the comparison is case sensitive. The proxy will route the request hostname in a case-insensitive way which means the authorization policy could be bypassed. As an example, the user may have an authorization policy that rejects request with hostname \"httpbin.foo\" for some source IPs, but the attacker can bypass this by sending the request with hostname \"Httpbin.Foo\". Patches are available in Istio 1.11.1, Istio 1.10.4 and Istio 1.9.8. As a work around a Lua filter may be written to normalize Host header before the authorization check. This is similar to the Path normalization presented in the [Security Best Practices](https://istio.io/latest/docs/ops/best-practices/security/#case-normalization) guide.","status":"published","published":"2021-08-24T23:15:07.093Z","modified":"2026-10-20T10:54:52.95724945Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","level":"high"}],"updated_at":"2026-11-02T15:44:20.843843Z"},{"id":"GHSA-7774-7vr3-cc8j","title":"Authorization Policy Bypass Due to Case Insensitive Host Comparison","description":"### Impact\nAccording to [RFC 4343](https://datatracker.ietf.org/doc/html/rfc4343), Istio authorization policy should compare the hostname in the HTTP Host header in a case insensitive way, but currently the comparison is case sensitive.  The Envoy proxy will route the request hostname in a case-insensitive way which means the authorization policy could be bypassed.\n \nAs an example, the user may have an authorization policy that rejects request with hostname \"httpbin.foo\" for some source IPs, but the attacker can bypass this by sending the request with hostname \"Httpbin.Foo\".\n\n### Patches\n* Istio 1.11.1 and above\n* Istio 1.10.4 and above\n* Istio 1.9.8 and above\n\n### Workarounds\nA Lua filter may be written to normalize Host header before the authorization check.  This is similar to the Path normalization presented in the [Security Best Practices](https://istio.io/latest/docs/ops/best-practices/security/#case-normalization) guide.\n\n### References\nMore details can be found in the [Istio Security Bulletin](https://istio.io/latest/news/security/istio-security-2021-008).\n\n### For more information\nIf you have any questions or comments about this advisory, please email us at istio-security-vulnerability-reports@googlegroups.com\n","status":"published","published":"2021-08-30T16:15:56Z","modified":"2026-09-10T03:49:07.371161372Z","cvss":[{"version":"3.1","score":8.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:L","level":"high"}],"cwes":["CWE-178"],"updated_at":"2026-11-02T15:46:40.657155Z"},{"id":"RHSA-2021:3272","title":"Red Hat Security Advisory: Red Hat OpenShift Service Mesh 2.0.7.1 security update","status":"published","published":"2024-09-16T06:20:24Z","modified":"2026-03-18T11:31:14.624752Z","cvss":[{"version":"3.1","score":8.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L","level":"high"}],"updated_at":"2026-11-02T15:53:08.619234Z"},{"id":"RHSA-2021:3273","title":"Red Hat Security Advisory: Red Hat OpenShift Service Mesh 1.1.17.1 security update","status":"published","published":"2024-09-16T06:20:31Z","modified":"2026-03-18T11:31:15.902321Z","cvss":[{"version":"3.1","score":8.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L","level":"high"}],"updated_at":"2026-11-02T15:53:08.619234Z"}]}}