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Environment variables still accessible through /proc

Moderate
cd-work published GHSA-wj7f-468m-6mv8 Dec 1, 2023

Package

cargo birdcage (Rust)

Affected versions

< 0.7.0

Patched versions

0.7.0

Description

Impact

Environment variables can be read from procfs unless a new process is started.

PoC

use birdcage::{Birdcage, Sandbox};
use std::{env, fs};

fn main() {
    Birdcage::new().lock().unwrap();

    assert_eq!(env::var_os("SECRET"), None);

    let environ = fs::read_to_string("/proc/self/environ").unwrap();
    assert!(!environ.contains("SECRET"), "ENVIRON CONTAINS SECRET:\n{environ}");
}
$  SECRET=test cargo run
thread 'main' panicked at src/main.rs:10:5:
ENVIRON CONTAINS SECRET:
 [truncated]

Possible Solutions

The simplest solution would be relying on the ptrace isolation and always spawning a new process by changing birdcage's API to create a new command. With an additional PID namespace the guarantees could be even further reinforced.

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Local
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

CVE ID

No known CVE

Weaknesses

No CWEs