Distribution advisory
This page covers CVE-2025-12543 as tracked by Ubuntu, for the package undertow. The fix is available in version 2.3.20-1ubuntu1; earlier versions remain affected.
How this vulnerability can be exploited
This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. A user must be tricked into taking some action. The scope is changed, meaning a successful attack can affect components beyond the vulnerable one. Rated impact: confidentiality high, integrity high, availability high.
CVSS metrics in full
The score comes from this vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
- Attack vector: Network — reachable from anywhere that can route to the service.
- Attack complexity: Low — the attack works reliably, with no preparation.
- Privileges required: None — an unauthenticated stranger can try it.
- User interaction: Required — someone has to click, open or visit something.
- Scope: Changed — a successful attack reaches components beyond the vulnerable one.
- Confidentiality impact: High — total loss, or loss the attacker controls.
- Integrity impact: High — total loss, or loss the attacker controls.
- Availability impact: High — total loss, or loss the attacker controls.
Weakness class
UBUNTU-CVE-2025-12543 is classified as CWE-20: Improper Input Validation. The application accepts input without checking that it has the expected form, so malformed values reach code that assumes they are well formed.
Affected software
UBUNTU-CVE-2025-12543 is recorded against 1 package.
- undertow (fixed in 2.3.20-1ubuntu1)
Timeline and source
Published on 7 January 2026 and last revised on 20 May 2026. No public exploit is currently recorded for this entry. Record sourced from OSV.
References
ubuntu.com (Report)
www.cve.org (Report)
access.redhat.com (Report)
bugzilla.redhat.com (Report)
github.com (Report)
github.com (Report)
github.com (Report)
github.com (Report)
ubuntu.com (Advisory)
Other advisories for this package
undertow has other advisories on record. If you are patching this one, these are worth checking on the same host:
Same weakness in other software
These advisories are the same class of weakness (CWE-20: Improper Input Validation) in other software:
