Skip to main content
veriom
Menu

Explore Veriom products, resources, and account pages.

CVE-2021-39144XStream Remote Code Execution Vulnerability

Patch nowHigh8.5Exploited, CISA due date 2023-03-31EPSS 98%, higher than 100% of scored CVEs

CVE-2021-39144 is a missing authentication in XStream, rated high (8.5 on CVSS 3.1).

Why this priority: Exploited in the wild: listed in CISA's KEV catalog.

Published · Updated · NVD status: Analyzed

What it is

A function that should require sign-in can be called by anyone. Serialized objects from outside are turned back into live objects, which a crafted payload can abuse to run code.

How it is reached

An attacker can exploit it over the network, with an ordinary user account, and nobody has to click anything. Success also depends on conditions the attacker does not fully control.

What an attacker gains

A successful attack can read the data it protects, change data or behaviour and take it offline. In practice, this kind of flaw lets an attacker act as a signed-in user, or an administrator, without valid credentials. The damage can spread past the vulnerable component into others.

Is it being exploited?

CISA added it to the Known Exploited Vulnerabilities catalog on 2023-03-10: it is being exploited in the wild. EPSS estimates a 98% chance of exploitation activity in the next 30 days, higher than 100% of scored CVEs.

What to do

  1. Treat it as urgent: it is on CISA's KEV list. CISA's deadline for US federal agencies: 2023-03-31.
  2. Upgrade XStream to 1.4.18 or later. The patch notes are linked below.
  3. Until it is patched, review who holds accounts that can reach it.
  4. Check exposed instances for signs of compromise, not only for the version.

Description from NVD

XStream is a simple library to serialize objects to XML and back again. In affected versions this vulnerability may allow a remote attacker has sufficient rights to execute commands of the host only by manipulating the processed input stream. No user is affected, who followed the recommendation to setup XStream's security framework with a whitelist limited to the minimal required types. XStream 1.4.18 uses no longer a blacklist by default, since it cannot be secured for general purpose.

What this means for your architecture.

A CVE names a product. Whether it matters depends on where that product sits in your systems: what reaches it, which trust boundary it guards and what it can reach once compromised. Veriom maps your components, their relationships and your trust boundaries from your code, cloud and delivery evidence, so you can see where a component like this sits. The radar itself does not look at your systems.

Components it touches

  • Operating systems on servers, workstations or devices. Everything on the host inherits the flaw.
  • Sign-in, session and token handling. The flaw sits between anonymous callers and authenticated sessions.
  • Identity providers and SSO. The flaw sits between anonymous callers and authenticated sessions.
  • APIs, queues and caches that accept serialized objects. The flaw sits between a message producer and the service that deserializes it.

Trust boundaries in play

  • Authenticated network access. An account is needed, so exposure follows who can sign in: customers, partners or staff.
  • Isolation between components. The impact crosses out of the vulnerable component into others it should be isolated from.
  • Between anonymous callers and authenticated sessions. An attacker who crosses it can act as a signed-in user, or an administrator, without valid credentials.
  • Between a message producer and the service that deserializes it. An attacker who crosses it can turn crafted data into code execution inside the receiving service.

Questions to answer about your own systems

  • Where does XStream run in your systems, and at which version?
  • Which of those instances can be reached from the internet or partner networks?
  • What can it reach once compromised: which data stores, secrets and services?
See how Veriom maps an architectureTake the interactive tour

Read more

Sources

  • CVE records and CVSS scores from the NVD CVE API. This product uses the NVD API but is not endorsed or certified by the NVD.
  • Exploitation status from CISA’s Known Exploited Vulnerabilities catalog.
  • Exploit likelihood from FIRST’s Exploit Prediction Scoring System (EPSS), refreshed daily.
  • Explanations are written by Veriom from fixed templates over each record’s data, not by a person reviewing each CVE. Descriptions are quoted from the records as published.