Summary
Sync-in Server has Username/Login Enumeration via Timing Side-Channel on POST /api/auth/login (incomplete fix of the prior timing-attack advisory)
validateUser() in backend/src/authentication/providers/mysql/auth-provider-mysql.service.ts returns immediately when the supplied login/email does not match any account, without ever calling comparePassword():
async validateUser(loginOrEmail: string, password: string, ip?: string, scope?: AUTH_SCOPE): Promise<UserModel> {
let user: UserModel
try {
user = await this.usersManager.findUser(loginOrEmail, false)
} catch (e) { ... }
if (!user) {
this.logger.warn(...)
return null // <-- comparePassword() is never reached here
}
return await this.usersManager.logUser(user, password, ip, scope)
}
comparePassword() (backend/src/common/functions.ts) already contains a dummy-hash branch that was clearly added to defend against exactly this class of attack:
export async function comparePassword(password: string, hash?: string | null): Promise<boolean> {
if (!hash) {
// No hash, waste time for time-based attacks
await bcrypt.compare(password, DUMMY_PASSWORD_HASH)
return false
}
return await bcrypt.compare(password, hash)
}
The problem is that this protection only runs when comparePassword() is actually invoked with a falsy hash. Because validateUser() short-circuits with return null as soon as findUser() comes back empty, the "account doesn't exist" path skips all cryptographic work entirely, while the "account exists, wrong password" path always performs a real bcrypt comparison (cost factor 10, ~100ms+). The two outcomes are trivially distinguishable by response time.
There's already a published advisory in this repo for "Username Enumeration via Timing Attack" - this looks like the same underlying issue surfacing through a different call path (the early return in validateUser()) that the existing fix (the dummy-hash branch in comparePassword()) doesn't actually reach, rather than a brand new vulnerability class.
Proof of Concept
Verified with the actual comparePassword() logic and the real DUMMY_PASSWORD_HASH constant copied verbatim from backend/src/common/functions.ts, using the project's own bcryptjs dependency (no mocking of bcrypt itself):
Avg time for "login does not exist" path (validateUser returns null, no bcrypt call): 0.00 ms
Avg time for "login exists, wrong password" path (real bcrypt.compare runs): 114.90 ms
Difference: 114.90 ms (ratio: ~58923x)
The "not found" path reproduces validateUser()'s exact early return (no call into comparePassword); the "wrong password" path reproduces logUser()'s real call into comparePassword(password, user.password). The gap is large enough to be trivially observable over a real network, even accounting for jitter.
Reachable endpoint: POST /api/auth/login, guarded only by AuthLocalGuard (Passport local strategy invoking validateUser()), no authentication required.
Impact
Any unauthenticated client can determine whether a given username/email is a valid account on the instance by timing POST /api/auth/login:
- Non-existent login: near-instant rejection (no bcrypt call).
- Existing login (regardless of password correctness): consistently slower due to a real bcrypt comparison.
This enables efficient enumeration of valid accounts, which can then be used to focus credential-stuffing, password-spraying, or phishing against confirmed-valid targets.
CVE-2026-58272 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.4.1); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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Make validateUser() always pass through comparePassword()'s timing-equalized path, even when no user is found, e.g.:
if (!user) {
await comparePassword(password, null) // burns the same time as a real comparison
return null
}
so the "account not found" and "account found, wrong password" branches take statistically indistinguishable time.
Frequently Asked Questions
- What is CVE-2026-58272? CVE-2026-58272 is a medium-severity security vulnerability in @sync-in/server (npm), affecting versions <= 2.4.0. It is fixed in 2.4.1.
- How severe is CVE-2026-58272? CVE-2026-58272 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of @sync-in/server are affected by CVE-2026-58272? @sync-in/server (npm) versions <= 2.4.0 is affected.
- Is there a fix for CVE-2026-58272? Yes. CVE-2026-58272 is fixed in 2.4.1. Upgrade to this version or later.
- Is CVE-2026-58272 exploitable, and should I be worried? Whether CVE-2026-58272 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-58272 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-58272? Upgrade
@sync-in/serverto 2.4.1 or later.