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CVE-2026-30923

libModSecurity3 denial of service via segfault when using t:hexDecode on single-character query strings

8.2 HighFix available

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. Libmodsecurity is one component of the ModSecurity v3 project. A segmentation fault occurs when a rule using the t:hexDecode transformation inspects a query string parameter containing a single character. An attacker can exploit this to crash worker processes, causing a denial of service. Service resumes once the attack stops as worker processes recover from the segfault. All versions before 3.0.15 of libModSecurity3 are affected. This has been patched in version 3.0.15.

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

0.43%Up 0.4 points since May 6, 2026
90%50%10%1%

What each source reports

CVE List Score used 8.2

libModSecurity3 denial of service via segfault when using t:hexDecode on single-character query strings

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. Libmodsecurity is one component of the ModSecurity v3 project. A segmentation fault occurs when a rule using the t:hexDecode transformation inspects a query string parameter containing a single character. An attacker can exploit this to crash worker processes, causing a denial of service. Service resumes once the attack stops as worker processes recover from the segfault. All versions before 3.0.15 of libModSecurity3 are affected. This has been patched in version 3.0.15.

Record
CVE-2026-30923
CVSS 4.0
8.2 HighCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Weakness
CWE-125
Updated
2026-11-02
EUVDEUVD-2026-27422 8.2

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. Libmodsecurity is one component of the ModSecurity v3 project. A segmentation fault occurs when a rule using the t:hexDecode transformation inspects a query string parameter containing a single character. An attacker can exploit this to crash worker processes, causing a denial of service. Service resumes once the attack stops as worker processes recover from the segfault. All versions before 3.0.15 of libModSecurity3 are affected. This has been patched in version 3.0.15.

Record
EUVD-2026-27422
CVSS 4.0
8.2 HighCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Updated
2026-11-02
NVD 8.2

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. Libmodsecurity is one component of the ModSecurity v3 project. A segmentation fault occurs when a rule using the t:hexDecode transformation inspects a query string parameter containing a single character. An attacker can exploit this to crash worker processes, causing a denial of service. Service resumes once the attack stops as worker processes recover from the segfault. All versions before 3.0.15 of libModSecurity3 are affected. This has been patched in version 3.0.15.

Record
CVE-2026-30923
CVSS 4.0
8.2 HighCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/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
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-125
Updated
2026-11-02
OSV 8.2

libModSecurity3 denial of service via segfault when using t:hexDecode on single-character query strings

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. Libmodsecurity is one component of the ModSecurity v3 project. A segmentation fault occurs when a rule using the t:hexDecode transformation inspects a query string parameter containing a single character. An attacker can exploit this to crash worker processes, causing a denial of service. Service resumes once the attack stops as worker processes recover from the segfault. All versions before 3.0.15 of libModSecurity3 are affected. This has been patched in version 3.0.15.

Record
CVE-2026-30923
CVSS 4.0
8.2 HighCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Weakness
CWE-125
Updated
2026-11-02
OSVDEBIAN-CVE-2026-30923 7.5

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. Libmodsecurity is one component of the ModSecurity v3 project. A segmentation fault occurs when a rule using the t:hexDecode transformation inspects a query string parameter containing a single character. An attacker can exploit this to crash worker processes, causing a denial of service. Service resumes once the attack stops as worker processes recover from the segfault. All versions before 3.0.15 of libModSecurity3 are affected. This has been patched in version 3.0.15.

Record
DEBIAN-CVE-2026-30923
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
OSVUBUNTU-CVE-2026-30923 8.2

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. Libmodsecurity is one component of the ModSecurity v3 project. A segmentation fault occurs when a rule using the t:hexDecode transformation inspects a query string parameter containing a single character. An attacker can exploit this to crash worker processes, causing a denial of service. Service resumes once the attack stops as worker processes recover from the segfault. All versions before 3.0.15 of libModSecurity3 are affected. This has been patched in version 3.0.15.

Record
UBUNTU-CVE-2026-30923
CVSS 4.0
8.2 HighCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
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 4 moreShow less
OSVAZL-85715 No score

CVE-2026-30923 affecting package mod_security 2.9.7-8

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. Libmodsecurity is one component of the ModSecurity v3 project. A segmentation fault occurs when a rule using the t:hexDecode transformation inspects a query string parameter containing a single character. An attacker can exploit this to crash worker processes, causing a denial of service. Service resumes once the attack stops as worker processes recover from the segfault. All versions before 3.0.15 of libModSecurity3 are affected. This has been patched in version 3.0.15.

Record
AZL-85715
Updated
2026-11-05
OSVBIT-modsecurity-2026-30923 No score

libModSecurity3 denial of service via segfault when using t:hexDecode on single-character query strings

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. Libmodsecurity is one component of the ModSecurity v3 project. A segmentation fault occurs when a rule using the t:hexDecode transformation inspects a query string parameter containing a single character. An attacker can exploit this to crash worker processes, causing a denial of service. Service resumes once the attack stops as worker processes recover from the segfault. All versions before 3.0.15 of libModSecurity3 are affected. This has been patched in version 3.0.15.

Record
BIT-modsecurity-2026-30923
Updated
2026-11-02
OSVBIT-modsecurity2-2026-30923 No score

libModSecurity3 denial of service via segfault when using t:hexDecode on single-character query strings

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. Libmodsecurity is one component of the ModSecurity v3 project. A segmentation fault occurs when a rule using the t:hexDecode transformation inspects a query string parameter containing a single character. An attacker can exploit this to crash worker processes, causing a denial of service. Service resumes once the attack stops as worker processes recover from the segfault. All versions before 3.0.15 of libModSecurity3 are affected. This has been patched in version 3.0.15.

Record
BIT-modsecurity2-2026-30923
Updated
2026-11-02
OSVopenSUSE-SU-2026:10732-1 No score

libmodsecurity3-3.0.15-1.1 on GA media

These are all security issues fixed in the libmodsecurity3-3.0.15-1.1 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2026:10732-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
mod_security
Azure Linux:3
 through 2.9.7-8 None known
modsecurity
Bitnami
 3.0.0 up to 3.0.15
3.0.15
modsecurity
Debian:12
 before 3.0.9-1+deb12u2, plus listed versions
3.0.9-13.0.9-1+deb12u1
3.0.9-1+deb12u2
modsecurity
Debian:13
 before 3.0.14-1+deb13u1, plus listed versions
3.0.14-1
3.0.14-1+deb13u1
modsecurity
Debian:14
 before 3.0.15-1, plus listed versions
3.0.14-1
3.0.15-1
modsecurity
Ubuntu:20.04:LTS
 All versions, plus listed versions
3.0.3-13.0.4-13.0.4-1build1
 None known
modsecurity
Ubuntu:22.04:LTS
 All versions, plus listed versions
3.0.4-23.0.6-1
 None known
modsecurity
Ubuntu:24.04:LTS
 All versions, plus listed versions
3.0.10-13.0.11-13.0.12-13.0.12-1.1build13.0.12-1.1build2
 None known
modsecurity
Ubuntu:25.10
 All versions, plus listed versions
3.0.13-13.0.14-13.0.14-1build1
 None known
modsecurity
Ubuntu:26.10
 All versions, plus listed versions
3.0.14-1build23.0.15-13.0.16-1
 None known
modsecurity
Ubuntu:26.04:LTS
 All versions, plus listed versions
3.0.14-1build13.0.14-1build2
 None known
modsecurity
openSUSE:Tumbleweed
From an advisory covering 2 CVEs
 before 3.0.15-1.1
3.0.15-1.1

History

History
RecordedChangedSources
affected
factsOSV
affected
first indexedCVE List, EUVD, NVD, OSV

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

In short

CVE-2026-30923 is a high vulnerability (CVSS 8.2) in Owasp Modsecurity, published May 5, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.43%, the 38th percentile. Fixed in modsecurity 3.0.15.

References

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