CVE-2024-39894

What it actually does

A logic error in ObscureKeystrokeTiming permits timing side-channel attacks that can leak information about keystrokes entered without echo during password prompts for utilities such as su and sudo.

Why it matters to the business

Successful exploitation can allow credential disclosure, enabling attackers to obtain elevated access and potentially compromise systems that rely on interactive authentication.

How an attack unfolds

An attacker observes measurable differences in processing time for password entry in affected OpenSSH versions to infer character content or length, then uses the recovered information to authenticate as the target user.

How to fix it

Upgrade OpenSSH to version 9.8 or later. On Debian 12 apply package version 6.1.85-1; on Debian 13 apply package version 6.7.12-1.

How to confirm the fix worked

Confirm the installed OpenSSH version is 9.8 or newer, or verify that the operating-system package versions match the listed fixed releases for the respective distribution.

Typical attack path

1. Locate systems running vulnerable OpenSSH versions between 9.5 and 9.7
2. Gain a vantage point allowing observation of network or local timing for authentication prompts
3. Trigger password entry for su, sudo, or similar commands
4. Measure and analyze timing variations to reconstruct password data
5. Authenticate using recovered credentials to escalate privileges

How to detect it

Examine system and authentication logs for repeated or unusual interactive login attempts around su or sudo usage; timing-based attacks themselves leave no distinctive artifacts in standard logs.

What your security team should do

• Apply the available package updates for OpenSSH on all affected Debian systems
• Review authentication configurations to reduce reliance on echo-off password entry where feasible
• Monitor authentication logs for anomalous patterns after patching