CVE-2026-23901 | Apache Shiro: Brute force attack possible to determine valid user names

Observable Timing Discrepancy vulnerability in Apache Shiro. This issue affects Apache Shiro: from 1.*, 2.* before 2.0.7. Users are recommended to upgrade to version 2.0.7 or later, which fixes the issue. Prior to Shiro 2.0.7, code paths for non-existent vs. existing users are different enough, that a brute-force attack may be able to tell, by timing the requests only, determine if the request failed because of a non-existent user vs. wrong password. The most likely attack vector is a local attack only. Shiro security model  https://shiro.apache.org/security-model.html#username_enumeration  discusses this as well. Typically, brute force attack can be mitigated at the infrastructure level.

Published: 2026-02-10 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-23901 is rated Low Risk (8.5/100): CVSS Low severity, with low exploitation likelihood (EPSS 0.22%). Low composite risk—no urgent action required; patch on your normal maintenance cycle and revisit priority if CVSS or EPSS increases.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-23901

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.01% 0.22% +0.21%
2 2026-02-10 — 0.01% —

Full EPSS history (2 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-23901

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
1.0 4.0 LOW
CVSS:4.0/AV:L/AC:H/AT:P/PR:L/UI:A/VC:L/VI:N/VA:N/SC:L/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:N/AU:Y/R:A/V:C/RE:L/U:Green Click to expand
Attack vector (AV:L)
Attacker needs local access on the target system.
Attack complexity (AC:H)
Exploitation depends on constrained or hard-to-reproduce conditions.
Attack requirements (AT:P)
Additional preconditions must be present for exploitation.
Privileges required (PR:L)
Low privileges are required.
User interaction (UI:A)
User interaction is required in an active way.
Vulnerable system confidentiality impact (VC:L)
Limited confidentiality impact on the vulnerable system.
Vulnerable system integrity impact (VI:N)
No integrity impact on the vulnerable system.
Vulnerable system availability impact (VA:N)
No availability impact on the vulnerable system.
Subsequent system confidentiality impact (SC:L)
Limited confidentiality impact on subsequent systems.
Subsequent system integrity impact (SI:N)
No integrity impact on subsequent systems.
Subsequent system availability impact (SA:N)
No availability impact on subsequent systems.
Exploit maturity (threat) (E:X)
Not defined: no reliable threat intelligence; scoring assumes the worst case (equivalent to Attacked).
Confidentiality requirement (CR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Integrity requirement (IR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Availability requirement (AR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Modified attack vector (MAV:X)
Not defined: scoring uses the Base Attack Vector (AV).
Modified attack complexity (MAC:X)
Not defined: scoring uses the Base Attack Complexity (AC).
Modified attack requirements (MAT:X)
Not defined: scoring uses the Base Attack Requirements (AT).
Modified privileges required (MPR:X)
Not defined: scoring uses the Base Privileges Required (PR).
Modified user interaction (MUI:X)
Not defined: scoring uses the Base User Interaction (UI).
Modified vulnerable system confidentiality impact (MVC:X)
Not defined: scoring uses the Base VC metric.
Modified vulnerable system integrity impact (MVI:X)
Not defined: scoring uses the Base VI metric.
Modified vulnerable system availability impact (MVA:X)
Not defined: scoring uses the Base VA metric.
Modified subsequent system confidentiality impact (MSC:X)
Not defined: scoring uses the Base SC metric.
Modified subsequent system integrity impact (MSI:X)
Not defined: scoring uses the Base SI metric.
Modified subsequent system availability impact (MSA:X)
Not defined: scoring uses the Base SA metric.
Safety (supplemental) (S:N)
Negligible: impact meets the IEC 61508 negligible safety consequence category.
Automatable (supplemental) (AU:Y)
Yes: all four kill-chain steps (reconnaissance, weaponization, delivery, exploitation) can be automated.
Recovery (supplemental) (R:A)
Automatic: services recover on their own after an attack.
Value density (supplemental) (V:C)
Concentrated: a single exploit event controls rich resources (e.g., a central server).
Vulnerability response effort (supplemental) (RE:L)
Low/trivial response effort (documentation, simple configuration, low-touch guidance).
Provider urgency (supplemental) (U:GREEN)
Green: provider rates reduced urgency.
 — — [email protected]
2.5 3.1 LOW
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 1.0 1.4 [email protected]

Weakness enumeration for CVE-2026-23901

GitHub Security Advisory for CVE-2026-23901

GHSA-c4qc-4q9p-m9q9 · Severity: low · Ecosystem: maven — Apache Shiro Affected by an Observable Timing Discrepancy Vulnerability

OS Trackers for CVE-2026-23901

vendor priority summary link
debian not yet assigned CVE-2026-23901 not yet assigned priority: Debian including 1 source packages (shiro), 4 status rows across 4 suites (bookworm, bullseye, sid, trixie): open 4. https://security-tracker.debian.org/tracker/CVE-2026-23901
redhat low — https://access.redhat.com/security/cve/CVE-2026-23901
ubuntu medium CVE-2026-23901 medium priority: Ubuntu including 1 source packages (shiro), 7 status rows across 7 suites (bionic, focal, jammy, noble, questing, upstream, xenial): needs-triage 7. https://ubuntu.com/security/CVE-2026-23901

Affected software / configurations for CVE-2026-23901

Vendor Product Version Raw CPE
apache shiro < 2.0.7 cpe:2.3:a:apache:shiro:*:*:*:*:*:*:*:*

References for CVE-2026-23901

URL Tags
https://lists.apache.org/thread/mm1jct9b86jvnh3y44tj22xvjtx3xhhh Issue Tracking Mailing List Third Party Advisory
http://www.openwall.com/lists/oss-security/2026/02/08/2 Mailing List Third Party Advisory
cvelogic Threat Intelligence