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CVE-2021-33194

golang.org/x/net/html Infinite Loop vulnerability

7.5 HighFix available

golang.org/x/net before v0.0.0-20210520170846-37e1c6afe023 allows attackers to cause a denial of service (infinite loop) via crafted ParseFragment input.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
None
Availability
High

Exploit likelihood

7.49%Up 7.1 points since May 27, 2021
90%50%10%1%

What each source reports

NVD Score used 7.5

golang.org/x/net before v0.0.0-20210520170846-37e1c6afe023 allows attackers to cause a denial of service (infinite loop) via crafted ParseFragment input.

Record
CVE-2021-33194
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS 2.0
5.0 MediumAV:N/AC:L/Au:N/C:N/I:N/A:P
Weakness
CWE-835
Updated
2026-11-02
CVE List No score

golang.org/x/net before v0.0.0-20210520170846-37e1c6afe023 allows attackers to cause a denial of service (infinite loop) via crafted ParseFragment input.

Record
CVE-2021-33194
Updated
2026-11-02
EUVDEUVD-2022-3094 No score

golang.org/x/net before v0.0.0-20210520170846-37e1c6afe023 allows attackers to cause a denial of service (infinite loop) via crafted ParseFragment input.

Record
EUVD-2022-3094
Updated
2026-11-03
GitHub AdvisoriesGHSA-83g2-8m93-v3w7 7.5

golang.org/x/net/html Infinite Loop vulnerability

Go through 1.15.12 and 1.16.x through 1.16.4 has a golang.org/x/net/html infinite loop via crafted ParseFragment input.

Record
GHSA-83g2-8m93-v3w7
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-835
Updated
2026-11-02
OSV 7.5

golang.org/x/net before v0.0.0-20210520170846-37e1c6afe023 allows attackers to cause a denial of service (infinite loop) via crafted ParseFragment input.

Record
CVE-2021-33194
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVDEBIAN-CVE-2021-33194 7.5

golang.org/x/net before v0.0.0-20210520170846-37e1c6afe023 allows attackers to cause a denial of service (infinite loop) via crafted ParseFragment input.

Record
DEBIAN-CVE-2021-33194
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
Show 6 moreShow less
OSVGHSA-83g2-8m93-v3w7 7.5

golang.org/x/net/html Infinite Loop vulnerability

Go through 1.15.12 and 1.16.x through 1.16.4 has a golang.org/x/net/html infinite loop via crafted ParseFragment input.

Record
GHSA-83g2-8m93-v3w7
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-835
Updated
2026-11-02
OSVUBUNTU-CVE-2021-33194 7.5

golang.org/x/net before v0.0.0-20210520170846-37e1c6afe023 allows attackers to cause a denial of service (infinite loop) via crafted ParseFragment input.

Record
UBUNTU-CVE-2021-33194
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVBIT-golang-2021-33194 No score

golang.org/x/net before v0.0.0-20210520170846-37e1c6afe023 allows attackers to cause a denial of service (infinite loop) via crafted ParseFragment input.

Record
BIT-golang-2021-33194
Updated
2026-11-02
OSVGO-2021-0238 No score

Infinite loop when parsing inputs in golang.org/x/net/html

An attacker can craft an input to ParseFragment that causes it to enter an infinite loop and never return.

Record
GO-2021-0238
Updated
2026-11-02
OSVUSN-8089-2 No score

golang-golang-x-net-dev vulnerabilities

USN-8089-1 fixed vulnerabilities in Go Networking. This update provides the corresponding update to code vendored in golang-golang-x-net-dev.

Original advisory details:

Bahruz Jabiyev, Tommaso Innocenti, Anthony Gavazzi, Steven Sprecher, and Kaan Onarlioglu discovered that servers using Go Networking could hang during shutdown if preempted by a fatal error. An attacker could possibly use this to cause a denial of service. This issue only affected Ubuntu 22.04 LTS. (CVE-2022-27664)

Arpad Ryszka and Jakob Ackermann discovered that a maliciously crafted stream could cause excessive CPU usage in Go Networking's HPACK decoder. An attacker could possibly use this to cause a denial of service. This issue only affected Ubuntu 22.04 LTS. (CVE-2022-41723)

Mohammad Thoriq Aziz discovered that Go Networking did not properly sanitize some text nodes. An attacker could possibly use this to execute arbitrary code. This issue only affected Ubuntu 22.04 LTS. (CVE-2023-3978)

Sean Ng discovered an error in Go Networking's HTML tag handling. An attacker could possibly use this to cause a denial of service. (CVE-2025-22872)

Guido Vranken and Jakub Ciolek discovered that a maliciously crafted HTML document could exhaust system resources on servers using Go Networking. An attacker could possibly use this to cause a denial of service. (CVE-2025-47911)

Guido Vranken discovered that a maliciously crafted HTML document could put servers using Go Networking into an infinite loop. An attacker could possibly use this to cause a denial of service. (CVE-2025-58190)

Record
USN-8089-2
Updated
2026-11-02
OSVUSN-8089-3 No score

adsys, juju-core, lxd vulnerabilities

USN-8089-1 fixed vulnerabilities in Go Networking. This update provides the corresponding update to code vendored in LXD, ADSys, and Juju Core.

Original advisory details:

Bahruz Jabiyev, Tommaso Innocenti, Anthony Gavazzi, Steven Sprecher, and Kaan Onarlioglu discovered that servers using Go Networking could hang during shutdown if preempted by a fatal error. An attacker could possibly use this to cause a denial of service. This issue only affected Ubuntu 22.04 LTS. (CVE-2022-27664)

Arpad Ryszka and Jakob Ackermann discovered that a maliciously crafted stream could cause excessive CPU usage in Go Networking's HPACK decoder. An attacker could possibly use this to cause a denial of service. This issue only affected Ubuntu 22.04 LTS. (CVE-2022-41723)

Mohammad Thoriq Aziz discovered that Go Networking did not properly sanitize some text nodes. An attacker could possibly use this to execute arbitrary code. This issue only affected Ubuntu 22.04 LTS. (CVE-2023-3978)

Sean Ng discovered an error in Go Networking's HTML tag handling. An attacker could possibly use this to cause a denial of service. (CVE-2025-22872)

Guido Vranken and Jakub Ciolek discovered that a maliciously crafted HTML document could exhaust system resources on servers using Go Networking. An attacker could possibly use this to cause a denial of service. (CVE-2025-47911)

Guido Vranken discovered that a maliciously crafted HTML document could put servers using Go Networking into an infinite loop. An attacker could possibly use this to cause a denial of service. (CVE-2025-58190)

Record
USN-8089-3
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
golang.org/x/net
Go
before 0.0.0-20210520170846-37e1c6afe023
0.0.0-20210520170846-37e1c6afe023
golang
Bitnami
before 1.15.12, 1.16.0 up to 1.16.4
1.15.121.16.4
golang-golang-x-net
Debian:12
before 1:0.0+git20210119.5f4716e+dfsg-4
1:0.0+git20210119.5f4716e+dfsg-4
golang-golang-x-net
Debian:13
before 1:0.0+git20210119.5f4716e+dfsg-4
1:0.0+git20210119.5f4716e+dfsg-4
golang-golang-x-net
Debian:14
before 1:0.0+git20210119.5f4716e+dfsg-4
1:0.0+git20210119.5f4716e+dfsg-4
lxd
Ubuntu:Pro:18.04:LTS
before 3.0.3-0ubuntu1~18.04.2+esm2, plus listed versions
2.18-0ubuntu62.19-0ubuntu12.20-0ubuntu32.20-0ubuntu42.21-0ubuntu1
Show 16 moreShow less
2.21-0ubuntu22.21-0ubuntu32.21-0ubuntu43.0.0~beta2-0ubuntu33.0.0~beta3-0ubuntu33.0.0~beta5-0ubuntu23.0.0~beta7-0ubuntu13.0.0-0ubuntu13.0.0-0ubuntu23.0.0-0ubuntu33.0.0-0ubuntu43.0.1-0ubuntu1~18.04.13.0.2-0ubuntu1~18.04.13.0.3-0ubuntu1~18.04.13.0.3-0ubuntu1~18.04.23.0.3-0ubuntu1~18.04.2+esm1
3.0.3-0ubuntu1~18.04.2+esm2
golang-golang-x-net-dev
Ubuntu:Pro:20.04:LTS
before 1:0.0+git20190811.74dc4d7+dfsg-1ubuntu0.1~esm2, plus listed versions
1:0.0+git20190811.74dc4d7+dfsg-11:0.0+git20190811.74dc4d7+dfsg-1ubuntu0.1~esm1
1:0.0+git20190811.74dc4d7+dfsg-1ubuntu0.1~esm2
golang-golang-x-net-dev
Ubuntu:Pro:16.04:LTS
before 1:0.0+git20160110.4fd4a9f-1ubuntu0.1~esm2, plus listed versions
0.0+git20150226.3d87fd6-30.0+git20151007.b846920+dfsg-11:0.0+git20150817.66f0418-11:0.0+git20160110.4fd4a9f-11:0.0+git20160110.4fd4a9f-1ubuntu0.1~esm1
1:0.0+git20160110.4fd4a9f-1ubuntu0.1~esm2
golang-golang-x-net-dev
Ubuntu:Pro:18.04:LTS
before 1:0.0+git20170629.c81e7f2+dfsg-2ubuntu0.1~esm2, plus listed versions
1:0.0+git20170629.c81e7f2+dfsg-1ubuntu11:0.0+git20170629.c81e7f2+dfsg-1ubuntu21:0.0+git20170629.c81e7f2+dfsg-21:0.0+git20170629.c81e7f2+dfsg-2ubuntu0.1~esm1
1:0.0+git20170629.c81e7f2+dfsg-2ubuntu0.1~esm2
juju-core
Ubuntu:Pro:16.04:LTS
before 2.3.7-0ubuntu0.16.04.1+esm2, plus listed versions
1.24.6-0ubuntu31.25.0-0ubuntu11.25.0-0ubuntu21.25.0-0ubuntu32.0~beta4-0ubuntu2
Show 11 moreShow less
2.0~beta6-0ubuntu1.16.04.12.0~beta7-0ubuntu1.16.04.12.0~beta12-0ubuntu1.16.04.12.0~beta15-0ubuntu2.16.04.12.0.0-0ubuntu0.16.04.22.0.2-0ubuntu0.16.04.12.0.2-0ubuntu0.16.04.22.3.1-0ubuntu0.16.04.12.3.2-0ubuntu0.16.04.12.3.7-0ubuntu0.16.04.12.3.7-0ubuntu0.16.04.1+esm1
2.3.7-0ubuntu0.16.04.1+esm2
lxd
Ubuntu:Pro:16.04:LTS
before 2.0.11-0ubuntu1~16.04.4+esm2, plus listed versions
0.20-0ubuntu40.21-0ubuntu30.21-0ubuntu50.22-0ubuntu10.22-0ubuntu2
Show 45 moreShow less
0.23-0ubuntu10.23-0ubuntu20.23-0ubuntu30.24-0ubuntu20.24-0ubuntu30.24-0ubuntu40.25-0ubuntu10.26-0ubuntu20.26-0ubuntu30.27-0ubuntu10.27-0ubuntu22.0.0~beta1-0ubuntu32.0.0~beta1-0ubuntu42.0.0~beta2-0ubuntu12.0.0~beta2-0ubuntu22.0.0~beta3-0ubuntu12.0.0~beta3-0ubuntu22.0.0~beta3-0ubuntu32.0.0~beta3-0ubuntu42.0.0~beta4-0ubuntu12.0.0~beta4-0ubuntu22.0.0~beta4-0ubuntu32.0.0~beta4-0ubuntu42.0.0~beta4-0ubuntu52.0.0~beta4-0ubuntu62.0.0~beta4-0ubuntu72.0.0~rc1-0ubuntu12.0.0~rc1-0ubuntu22.0.0~rc1-0ubuntu32.0.0~rc2-0ubuntu22.0.0~rc2-0ubuntu32.0.0~rc3-0ubuntu12.0.0~rc3-0ubuntu22.0.0~rc3-0ubuntu32.0.0~rc3-0ubuntu42.0.0~rc4-0ubuntu12.0.0~rc5-0ubuntu12.0.0~rc6-0ubuntu12.0.0~rc6-0ubuntu22.0.0~rc7-0ubuntu12.0.0~rc7-0ubuntu22.0.0~rc8-0ubuntu12.0.0~rc8-0ubuntu22.0.0~rc8-0ubuntu32.0.0~rc8-0ubuntu5
2.0.11-0ubuntu1~16.04.4+esm2
adsys
Ubuntu:Pro:20.04:LTS
before 0.9.2~20.04.2ubuntu0.1+esm1, plus listed versions
0.8~22.040.9.2~20.040.9.2~20.04.10.9.2~20.04.20.9.2~20.04.2ubuntu0.1
0.9.2~20.04.2ubuntu0.1+esm1

History

History
RecordedChangedSources
aliasesEUVD
first indexedCVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-33194 is a high vulnerability (CVSS 7.5) in Golang Go, published May 26, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 7.49%, the 94th percentile. Fixed in golang.org/x/net 0.0.0-20210520170846-37e1c6afe023.

References

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