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CVE-2026-33170

Rails Active Support has a possible XSS vulnerability in SafeBuffer#%

5.3 MediumFix available

Active Support is a toolkit of support libraries and Ruby core extensions extracted from the Rails framework. Prior to versions 8.1.2.1, 8.0.4.1, and 7.2.3.1, SafeBuffer#% does not propagate the @html_unsafe flag to the newly created buffer. If a SafeBuffer is mutated in place (e.g. via gsub!) and then formatted with % using untrusted arguments, the result incorrectly reports html_safe? == true, bypassing ERB auto-escaping and possibly leading to XSS. Versions 8.1.2.1, 8.0.4.1, and 7.2.3.1 contain a patch.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
Passive

What an attacker can affect

Confidentiality
None
Integrity
Low
Availability
None

Exploit likelihood

0.34%Up 0.3 points since Mar 24, 2026
90%50%10%1%

What each source reports

CVE List Score used 5.3

Rails Active Support has a possible XSS vulnerability in SafeBuffer#%

Active Support is a toolkit of support libraries and Ruby core extensions extracted from the Rails framework. Prior to versions 8.1.2.1, 8.0.4.1, and 7.2.3.1, SafeBuffer#% does not propagate the @html_unsafe flag to the newly created buffer. If a SafeBuffer is mutated in place (e.g. via gsub!) and then formatted with % using untrusted arguments, the result incorrectly reports html_safe? == true, bypassing ERB auto-escaping and possibly leading to XSS. Versions 8.1.2.1, 8.0.4.1, and 7.2.3.1 contain a patch.

Record
CVE-2026-33170
CVSS 4.0
5.3 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
Weakness
CWE-79
Updated
2026-11-02
EUVDEUVD-2026-14624 5.3

Active Support is a toolkit of support libraries and Ruby core extensions extracted from the Rails framework. Prior to versions 8.1.2.1, 8.0.4.1, and 7.2.3.1, SafeBuffer#% does not propagate the @html_unsafe flag to the newly created buffer. If a SafeBuffer is mutated in place (e.g. via gsub!) and then formatted with % using untrusted arguments, the result incorrectly reports html_safe? == true, bypassing ERB auto-escaping and possibly leading to XSS. Versions 8.1.2.1, 8.0.4.1, and 7.2.3.1 contain a patch.

Record
EUVD-2026-14624
CVSS 4.0
5.3 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
Updated
2026-11-02
GitHub AdvisoriesGHSA-89vf-4333-qx8v 5.3

Rails Active Support has a possible XSS vulnerability in SafeBuffer#%

Impact

SafeBuffer#% does not propagate the @html_unsafe flag to the newly created buffer. If a SafeBuffer is mutated in place (e.g. via gsub!) and then formatted with % using untrusted arguments, the result incorrectly reports html_safe? == true, bypassing ERB auto-escaping and possibly leading to XSS.

Releases

The fixed releases are available at the normal locations.

Credit

This issue was responsibly reported by @ch4n3-yoon

Record
GHSA-89vf-4333-qx8v
CVSS 4.0
5.3 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
Weakness
CWE-79
Updated
2026-11-02
NVD 5.3

Active Support is a toolkit of support libraries and Ruby core extensions extracted from the Rails framework. Prior to versions 8.1.2.1, 8.0.4.1, and 7.2.3.1, SafeBuffer#% does not propagate the @html_unsafe flag to the newly created buffer. If a SafeBuffer is mutated in place (e.g. via gsub!) and then formatted with % using untrusted arguments, the result incorrectly reports html_safe? == true, bypassing ERB auto-escaping and possibly leading to XSS. Versions 8.1.2.1, 8.0.4.1, and 7.2.3.1 contain a patch.

Record
CVE-2026-33170
CVSS 4.0
5.3 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CVSS 3.1
6.1 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Weakness
CWE-79
Updated
2026-11-02
OSV 5.3

Rails Active Support has a possible XSS vulnerability in SafeBuffer#%

Active Support is a toolkit of support libraries and Ruby core extensions extracted from the Rails framework. Prior to versions 8.1.2.1, 8.0.4.1, and 7.2.3.1, SafeBuffer#% does not propagate the @html_unsafe flag to the newly created buffer. If a SafeBuffer is mutated in place (e.g. via gsub!) and then formatted with % using untrusted arguments, the result incorrectly reports html_safe? == true, bypassing ERB auto-escaping and possibly leading to XSS. Versions 8.1.2.1, 8.0.4.1, and 7.2.3.1 contain a patch.

Record
CVE-2026-33170
CVSS 4.0
5.3 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
Weakness
CWE-79
Updated
2026-11-02
OSVDEBIAN-CVE-2026-33170 6.1

Active Support is a toolkit of support libraries and Ruby core extensions extracted from the Rails framework. Prior to versions 8.1.2.1, 8.0.4.1, and 7.2.3.1, SafeBuffer#% does not propagate the @html_unsafe flag to the newly created buffer. If a SafeBuffer is mutated in place (e.g. via gsub!) and then formatted with % using untrusted arguments, the result incorrectly reports html_safe? == true, bypassing ERB auto-escaping and possibly leading to XSS. Versions 8.1.2.1, 8.0.4.1, and 7.2.3.1 contain a patch.

Record
DEBIAN-CVE-2026-33170
CVSS 3.1
6.1 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Updated
2026-11-02
OSVGHSA-89vf-4333-qx8v 5.3

Rails Active Support has a possible XSS vulnerability in SafeBuffer#%

Impact

SafeBuffer#% does not propagate the @html_unsafe flag to the newly created buffer. If a SafeBuffer is mutated in place (e.g. via gsub!) and then formatted with % using untrusted arguments, the result incorrectly reports html_safe? == true, bypassing ERB auto-escaping and possibly leading to XSS.

Releases

The fixed releases are available at the normal locations.

Credit

This issue was responsibly reported by @ch4n3-yoon

Record
GHSA-89vf-4333-qx8v
CVSS 4.0
5.3 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
Weakness
CWE-79
Updated
2026-11-02
OSVUBUNTU-CVE-2026-33170 5.3

Active Support is a toolkit of support libraries and Ruby core extensions extracted from the Rails framework. Prior to versions 8.1.2.1, 8.0.4.1, and 7.2.3.1, SafeBuffer#% does not propagate the @html_unsafe flag to the newly created buffer. If a SafeBuffer is mutated in place (e.g. via gsub!) and then formatted with % using untrusted arguments, the result incorrectly reports html_safe? == true, bypassing ERB auto-escaping and possibly leading to XSS. Versions 8.1.2.1, 8.0.4.1, and 7.2.3.1 contain a patch.

Record
UBUNTU-CVE-2026-33170
CVSS 4.0
5.3 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
CVSS 3.1
6.1 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
activesupport
RubyGems
 8.1.0.beta1 up to 8.1.2.1
8.1.2.1
activesupport
RubyGems
 8.0.0.beta1 up to 8.0.4.1
8.0.4.1
activesupport
RubyGems
 before 7.2.3.1
7.2.3.1
rails
Debian:12
 before 2:6.1.7.10+dfsg-1~deb12u3, plus listed versions
2:6.1.7.10+dfsg-1~deb12u12:6.1.7.10+dfsg-1~deb12u22:6.1.7.3+dfsg-12:6.1.7.3+dfsg-102:6.1.7.3+dfsg-11
Show 12 moreShow less
2:6.1.7.3+dfsg-122:6.1.7.3+dfsg-132:6.1.7.3+dfsg-22:6.1.7.3+dfsg-2~deb12u12:6.1.7.3+dfsg-32:6.1.7.3+dfsg-42:6.1.7.3+dfsg-52:6.1.7.3+dfsg-62:6.1.7.3+dfsg-72:6.1.7.3+dfsg-7~exp12:6.1.7.3+dfsg-82:6.1.7.3+dfsg-9
2:6.1.7.10+dfsg-1~deb12u3
rails
Debian:13
 before 2:7.2.2.2+dfsg-2~deb13u2, plus listed versions
2:7.2.2.1+dfsg-72:7.2.2.2+dfsg-12:7.2.2.2+dfsg-2~deb13u1
2:7.2.2.2+dfsg-2~deb13u2
rails
Debian:14
 before 2:7.2.3.1+dfsg-1, plus listed versions
2:7.2.2.1+dfsg-72:7.2.2.2+dfsg-12:7.2.2.2+dfsg-22:7.2.2.2+dfsg-2~deb13u12:7.2.2.2+dfsg-2~deb13u22:7.2.3+dfsg-12:7.2.3+dfsg-22:7.2.3+dfsg-3
2:7.2.3.1+dfsg-1
activesupport
RubyGems
 8.1.0.beta1 up to 8.1.2.1, plus listed versions
8.1.08.1.0.rc18.1.18.1.2
8.1.2.1
activesupport
RubyGems
 8.0.0.beta1 up to 8.0.4.1, plus listed versions
8.0.08.0.0.18.0.0.rc18.0.0.rc28.0.1
Show 4 moreShow less
8.0.28.0.2.18.0.38.0.4
8.0.4.1
activesupport
RubyGems
 before 7.2.3.1, plus listed versions
1.0.01.0.11.0.21.0.31.0.4
Show 45 moreShow less
1.1.01.1.11.2.11.2.21.2.31.2.41.2.51.3.01.3.11.4.01.4.11.4.21.4.31.4.42.0.02.0.12.0.22.0.42.0.52.1.02.1.12.1.22.2.22.2.32.3.102.3.112.3.122.3.142.3.152.3.162.3.172.3.182.3.22.3.32.3.42.3.52.3.62.3.6.pre2.3.72.3.82.3.8.pre12.3.92.3.9.pre3.0.03.0.0.beta
7.2.3.1
rails
Ubuntu:Pro:16.04:LTS
 All versions, plus listed versions
2:4.1.10-12:4.2.5-12:4.2.5.1-12:4.2.5.2-22:4.2.6-12:4.2.6-1ubuntu0.1~esm12:4.2.6-1ubuntu0.1~esm2
 None known
Show 7 moreShow less
Affected packages
PackageAffectedFixed
rails
Ubuntu:Pro:18.04:LTS
 All versions, plus listed versions
2:4.2.9-22:4.2.9-42:4.2.10-0ubuntu42:4.2.10-0ubuntu4+esm12:4.2.10-0ubuntu4+esm2
 None known
rails
Ubuntu:Pro:20.04:LTS
 All versions, plus listed versions
2:5.2.2.1+dfsg-1ubuntu12:5.2.3+dfsg-32:5.2.3+dfsg-3ubuntu0.1~esm1
 None known
rails
Ubuntu:Pro:22.04:LTS
 All versions, plus listed versions
2:6.0.3.7+dfsg-22:6.1.4.1+dfsg-8ubuntu22:6.1.4.1+dfsg-8ubuntu2+esm1
 None known
rails
Ubuntu:24.04:LTS
 All versions, plus listed versions
2:6.1.7.3+dfsg-2build12:6.1.7.3+dfsg-3
 None known
rails
Ubuntu:25.10
 All versions, plus listed versions
2:6.1.7.3+dfsg-72:7.2.2.1+dfsg-7
 None known
rails
Ubuntu:26.10
 All versions, plus listed versions
2:7.2.3+dfsg-22:7.2.3.2+dfsg-2
 None known
rails
Ubuntu:26.04:LTS
 All versions, plus listed versions
2:7.2.2.1+dfsg-72:7.2.2.2+dfsg-22:7.2.3+dfsg-2
 None known

History

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

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

In short

CVE-2026-33170 is a medium vulnerability (CVSS 5.3) in Rubyonrails Rails, published March 23, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.34%, the 27th percentile. Fixed in activesupport 8.1.2.1.

References

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