# CVE-2021-33620: squid: Squid before 4.15 and 5.x before 5.0.6 allows remote servers to cause adenial of service (affecting availability to a... CVE-2021-33620 is fixed in 9 products on 1 platform, first by squid 3.5.27-1ubuntu1.11, released May 28, 2021. It is not reported as exploited. Patch Radar priority: High. - Web page: https://patchblox.com/security/cve/CVE-2021-33620 - Priority: High - CVSS: 7.4 (Medium) - EPSS: 0.7958 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: May 28, 2021 ## Description Squid before 4.15 and 5.x before 5.0.6 allows remote servers to cause adenial of service (affecting availability to all clients) via an HTTPresponse. The issue trigger is a header that can be expected to exist inHTTP traffic without any malicious intent by the server. ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Linux | libecap RHEL 8 | 0:1.0.1-2.module+el8.1.0+4044+36416a77 | [RHSA-2021:4292](https://patchblox.com/security/data/fix/linux/rhsa-2021-4292.md) | Nov 9, 2021 | | Linux | libecap almalinux 8 | 1.0.1-2.module_el8.6.0+2741+01592ae8 | [ALSA-2021:4292](https://patchblox.com/security/data/fix/linux/alsa-2021-4292.md) | Nov 9, 2021 | | Linux | libecap ol 8 | 0:1.0.1-2.module+el8.3.0+7819+eb7d4ef6 | [ELSA-2021-4292](https://patchblox.com/security/data/fix/linux/elsa-2021-4292.md) | Nov 16, 2021 | | Linux | libecap rocky 8 | 0:1.0.1-2.module+el8.4.0+404+316a0dc5 | [RLSA-2021:4292](https://patchblox.com/security/data/fix/linux/rlsa-2021-4292.md) | Nov 9, 2021 | | Linux | libecap-devel RHEL 8 | 0:1.0.1-2.module+el8.1.0+4044+36416a77 | [RHSA-2021:4292](https://patchblox.com/security/data/fix/linux/rhsa-2021-4292.md) | Nov 9, 2021 | | Linux | libecap-devel almalinux 8 | 1.0.1-2.module_el8.6.0+2741+01592ae8 | [ALSA-2021:4292](https://patchblox.com/security/data/fix/linux/alsa-2021-4292.md) | Nov 9, 2021 | | Linux | libecap-devel ol 8 | 0:1.0.1-2.module+el8.3.0+7819+eb7d4ef6 | [ELSA-2021-4292](https://patchblox.com/security/data/fix/linux/elsa-2021-4292.md) | Nov 16, 2021 | | Linux | squid RHEL 8 | 7:4.15-1.module+el8.5.0+11469+24c223d9 | [RHSA-2021:4292](https://patchblox.com/security/data/fix/linux/rhsa-2021-4292.md) | Nov 9, 2021 | | Linux | squid Ubuntu 18.04.6 LTS (bionic) | 3.5.27-1ubuntu1.11 | [squid 3.5.27-1ubuntu1.11](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-squid-3.5.27-1ubuntu1.11.md) | May 28, 2021 | | Linux | squid Ubuntu 20.04 LTS (focal) | 4.10-1ubuntu1.4 | [squid 4.10-1ubuntu1.4](https://patchblox.com/security/data/fix/linux/ubuntu-focal-squid-4.10-1ubuntu1.4.md) | May 28, 2021 | | Linux | squid Ubuntu 24.10 (oracular) | 4.13-10ubuntu1 | [squid 4.13-10ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-oracular-squid-4.13-10ubuntu1.md) | Jan 16, 2026 | | Linux | squid Ubuntu 25.04 (plucky) | 4.13-10ubuntu1 | [squid 4.13-10ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-plucky-squid-4.13-10ubuntu1.md) | Jan 16, 2026 | | Linux | squid almalinux 8 | 7:4.15-3.module_el8.6.0+3010+383bc947.1 | [ALSA-2021:4292](https://patchblox.com/security/data/fix/linux/alsa-2021-4292.md) | Nov 9, 2021 | | Linux | squid ol 8 | 7:4.15-1.module+el8.5.0+20327+24c223d9 | [ELSA-2021-4292](https://patchblox.com/security/data/fix/linux/elsa-2021-4292.md) | Nov 16, 2021 | | Linux | squid rocky 8 | 7:4.15-1.module+el8.5.0+705+218dec94 | [RLSA-2021:4292](https://patchblox.com/security/data/fix/linux/rlsa-2021-4292.md) | Nov 9, 2021 | | Linux | squid-cgi Ubuntu 18.04.6 LTS (bionic) | 3.5.27-1ubuntu1.11 | [squid-cgi 3.5.27-1ubuntu1.11](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-squid-cgi-3.5.27-1ubuntu1.11.md) | May 28, 2021 | | Linux | squid-cgi Ubuntu 20.04 LTS (focal) | 4.10-1ubuntu1.4 | [squid-cgi 4.10-1ubuntu1.4](https://patchblox.com/security/data/fix/linux/ubuntu-focal-squid-cgi-4.10-1ubuntu1.4.md) | May 28, 2021 | | Linux | squid-cgi Ubuntu 24.10 (oracular) | 4.13-10ubuntu1 | [squid-cgi 4.13-10ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-oracular-squid-cgi-4.13-10ubuntu1.md) | Jan 16, 2026 | | Linux | squid-cgi Ubuntu 25.04 (plucky) | 4.13-10ubuntu1 | [squid-cgi 4.13-10ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-plucky-squid-cgi-4.13-10ubuntu1.md) | Jan 16, 2026 | | Linux | squid-common Ubuntu 18.04.6 LTS (bionic) | 3.5.27-1ubuntu1.11 | [squid-common 3.5.27-1ubuntu1.11](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-squid-common-3.5.27-1ubuntu1.11.md) | May 28, 2021 | | Linux | squid-common Ubuntu 20.04 LTS (focal) | 4.10-1ubuntu1.4 | [squid-common 4.10-1ubuntu1.4](https://patchblox.com/security/data/fix/linux/ubuntu-focal-squid-common-4.10-1ubuntu1.4.md) | May 28, 2021 | | Linux | squid-common Ubuntu 24.10 (oracular) | 4.13-10ubuntu1 | [squid-common 4.13-10ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-oracular-squid-common-4.13-10ubuntu1.md) | Jan 16, 2026 | | Linux | squid-common Ubuntu 25.04 (plucky) | 4.13-10ubuntu1 | [squid-common 4.13-10ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-plucky-squid-common-4.13-10ubuntu1.md) | Jan 16, 2026 | | Linux | squid-openssl Ubuntu 24.10 (oracular) | 4.13-10ubuntu1 | [squid-openssl 4.13-10ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-oracular-squid-openssl-4.13-10ubuntu1.md) | Jan 16, 2026 | | Linux | squid-openssl Ubuntu 25.04 (plucky) | 4.13-10ubuntu1 | [squid-openssl 4.13-10ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-plucky-squid-openssl-4.13-10ubuntu1.md) | Jan 16, 2026 | | Linux | squid-purge Ubuntu 18.04.6 LTS (bionic) | 3.5.27-1ubuntu1.11 | [squid-purge 3.5.27-1ubuntu1.11](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-squid-purge-3.5.27-1ubuntu1.11.md) | May 28, 2021 | | Linux | squid-purge Ubuntu 20.04 LTS (focal) | 4.10-1ubuntu1.4 | [squid-purge 4.10-1ubuntu1.4](https://patchblox.com/security/data/fix/linux/ubuntu-focal-squid-purge-4.10-1ubuntu1.4.md) | May 28, 2021 | | Linux | squid-purge Ubuntu 24.10 (oracular) | 4.13-10ubuntu1 | [squid-purge 4.13-10ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-oracular-squid-purge-4.13-10ubuntu1.md) | Jan 16, 2026 | | Linux | squid-purge Ubuntu 25.04 (plucky) | 4.13-10ubuntu1 | [squid-purge 4.13-10ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-plucky-squid-purge-4.13-10ubuntu1.md) | Jan 16, 2026 | | Linux | squid3 Ubuntu 18.04.6 LTS (bionic) | 3.5.27-1ubuntu1.11 | [squid3 3.5.27-1ubuntu1.11](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-squid3-3.5.27-1ubuntu1.11.md) | May 28, 2021 | | Linux | squidclient Ubuntu 18.04.6 LTS (bionic) | 3.5.27-1ubuntu1.11 | [squidclient 3.5.27-1ubuntu1.11](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-squidclient-3.5.27-1ubuntu1.11.md) | May 28, 2021 | | Linux | squidclient Ubuntu 20.04 LTS (focal) | 4.10-1ubuntu1.4 | [squidclient 4.10-1ubuntu1.4](https://patchblox.com/security/data/fix/linux/ubuntu-focal-squidclient-4.10-1ubuntu1.4.md) | May 28, 2021 | | Linux | squidclient Ubuntu 24.10 (oracular) | 4.13-10ubuntu1 | [squidclient 4.13-10ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-oracular-squidclient-4.13-10ubuntu1.md) | Jan 16, 2026 | | Linux | squidclient Ubuntu 25.04 (plucky) | 4.13-10ubuntu1 | [squidclient 4.13-10ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-plucky-squidclient-4.13-10ubuntu1.md) | Jan 16, 2026 | --- Data as of 2026-11-09T01:18:40Z UTC. 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