CVE-2026-33983 FreeRDP: Progressive Codec Quant BYTE Underflow - UB + CPU DoS
An attacker can cause a CPU denial of service in FreeRDP by triggering an infinite loop via a specific byte underflow in the progressive codec.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-33983?
CVE-2026-33983 is a medium-severity denial of service vulnerability in Freerdp Freerdp, published on 30 Mar 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
FreeRDP is a free implementation of the Remote Desktop Protocol. Prior to version 3.24.2, progressive_decompress_tile_upgrade() detects a mismatch via progressive_rfx_quant_cmp_equal() but only emits WLog_WARN, execution continues. The wrapped value (247) is used as a shift exponent, causing undefined behavior and an approximately 80 billion iteration loop (CPU DoS). This issue has been patched in version 3.24.2.
Which versions are affected by CVE-2026-33983?
It affects 1 product.
Products include Freerdp Freerdp.
How do I fix CVE-2026-33983?
Upgrade to a fixed version.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-33983 being exploited?
There is no known exploitation of CVE-2026-33983 in the wild and no public exploit code.
Other vulnerabilities in Freerdp Freerdp
- CVE-2021-37594 Other in n/a
- CVE-2021-37595 Other in n/a
- CVE-2026-67305 FreeRDP Windows Client before 3.29.0 Heap Buffer Overflow via Cliprdr
- CVE-2026-66402 FreeRDP before 3.29.0 TLS Certificate Identity Validation Bypass
- CVE-2026-67289 FreeRDP before 3.29.0 HTTP Proxy Request Injection via Redirection
Sources
Also known as DEBIAN-CVE-2026-33983, GHSA-4gfm-4p52-h478, UBUNTU-CVE-2026-33983.