`CVE-2026-55549`

Severity	6.5 Medium CVSS 3.1
Fixed in	`5.9.4`
Weakness	Cross-site scripting (CWE-79)
Published	28 Aug 2026
Updated	8 Sep 2026

Published 2 months ago. NVD often adds the list of affected products days or weeks after a CVE is published, and the other sources we check lag too. The scope and status here may change.

Description

Yamcs is a mission control framework. Prior to 5.9.4, Yamcs reflects an attacker-controlled redirect_uri parameter from GET /auth/authorize into yamcs-core/src/main/resources/auth/templates/authorize.html without adequate HTML escaping by yamcs-core/src/main/java/org/yamcs/http/auth/AuthHandler.java and yamcs-core/src/main/java/org/yamcs/http/HandlerContext.java. A crafted authorization URL can execute JavaScript when opened by a Yamcs user. The script can access browser-held authentication material and transmit it to an attacker, enabling account compromise. This issue is fixed in version 5.9.4.

Exploitation status

Working exploit published

A reviewed exploit catalogue lists ready-to-run exploit code for this CVE.

CISA KEV not listed
VulnCheck KEV not listed
CISA Vulnrichment exploitation: poc CISA recorded that an exploit has been demonstrated. Automatable: no, technical impact: partial.
Indexed PoC 1 indexed Published artifacts you can open, in Nuclei.
EPSS 1.3% chance in 30 days

Index	Artifact	Stars	First seen
Nuclei	Yamcs <=5.8.6 - Cross-Site Scripting

Index

Artifact

Stars

First seen

Nuclei

Yamcs <=5.8.6 - Cross-Site Scripting

Waratek protection

Mitigation candidate

A kind of vulnerability Waratek's rules address, with exploit code published or exploitation reported. No rule exists and none is planned yet. The decision below says what we found to build a rule from.

Protection none
Action unverified
Review automated Inferred
Record active

Decided by	A reference pointing at the upstream fix: a commit, a PR, a Red Hat bug
Finding	A reference points at an upstream fix (commit tier): https://github.com/yamcs/yamcs/commit/4d47d5cdcf5d92c2c5bbbc19feada422923332e3. That makes this CVE a candidate for an ARMR patch rule — it is the kind of defect ARMR can address, and there is a fix to work from. No rule exists and none is scheduled: writing one means reading the linked change and finding a hook point ARMR can express it at, which may turn out not to exist.
Candidate fix	https://github.com/yamcs/yamcs/commit/4d47d5cdcf5d92c2c5bbbc19feada422923332e3 : a commit: the change itself

Decided by

A reference pointing at the upstream fix: a commit, a PR, a Red Hat bug

Finding

A reference points at an upstream fix (commit tier): https://github.com/yamcs/yamcs/commit/4d47d5cdcf5d92c2c5bbbc19feada422923332e3. That makes this CVE a candidate for an ARMR patch rule — it is the kind of defect ARMR can address, and there is a fix to work from. No rule exists and none is scheduled: writing one means reading the linked change and finding a hook point ARMR can express it at, which may turn out not to exist.

Candidate fix

https://github.com/yamcs/yamcs/commit/4d47d5cdcf5d92c2c5bbbc19feada422923332e3 : a commit: the change itself

Affected software and releases

Maven packages

Affected and fixed versions, from OSV.dev

Package Introduced Fixed Last affected

org.yamcs:yamcs-core 0 5.9.4 unbounded

Package	Introduced	Fixed	Last affected
`org.yamcs:yamcs-core`	0	`5.9.4`	unbounded

Products and versions

1 product, 1 version entry

Source	Vendor	Product	Scheme	Affected versions
osv	org.yamcs	yamcs-core	generic	＜ 5.9.4

Source

Vendor

Product

Scheme

Affected versions

osv

org.yamcs

yamcs-core

generic

＜ 5.9.4

References

URL	Tags
https://github.com/yamcs/yamcs/commit/4d47d5cdcf5d92c2c5bbbc19feada422923332e3	commit
https://github.com/yamcs/yamcs/security/advisories/GHSA-rxpg-wjf8-qv9c	WEB
https://github.com/yamcs/yamcs	PACKAGE
https://github.com/yamcs/yamcs/releases/tag/yamcs-5.9.4	WEB

URL

Timeline

Published	2026-08-28	By the CVE Program.
NVD record modified	2026-09-08	NVD's own last-modified date for this record.

Published

2026-08-28

By the CVE Program.

NVD record modified

2026-09-08

NVD's own last-modified date for this record.

How VRT decided (17 of 24 rules ran)

17 of 24 rules ran. The rest didn't run because an earlier rule had already settled the CVE.

# Rule Outcome Status Detail

identity: Does this identifier describe a vulnerability at all? the first rule that matches decides

1 rejected no match CVE Program withdrawal of this identifier

scope: Is it a vulnerability Waratek protects? the first rule that matches decides

2 armr-patch-file no match An ARMR patch file on disk for this CVE

3 armr-secure-rule-file no match An ARMR security-rule template on disk for this CVE

4 manual-classification no match A researcher's recorded decision for this specific CVE

5 manual classification no match Manual classification of this CVE in the legacy dataset

6 non-java-upstream no match A root cause in non-Java code: an OS kernel, a C library, or a bundled runtime

7 oracle-component no match The defect being in a component of a tracked product the agent does not reach: JavaFX, the Java SE installer, the JInitiator browser plug-in, the native WebLogic proxy plug-in, or a native part of Oracle Application Server or Collaboration Suite (HTTP Server, Web Cache, Internet Directory, mail and calendar servers). Oracle gives these no CPE of their own and names them only in the description.

8 java-client-side no match Oracle's own risk-matrix note saying the CVE is reached only through untrusted code in the Java sandbox (applets, Web Start) or only through a client installation of Java, so a server running its own trusted code is not exposed

9 osv-maven matched In scope Maven packages: org.yamcs:yamcs-core

10 cna-maven-package not reached An affected Maven artifact named by the CNA itself

11 known-cpe-product not reached An NVD CPE naming a product ARMR tracks

12 cna-cpe-product not reached A CPE the CNA published naming a tracked product. Oracle publishes these on advisory day, months before NVD.

13 oracle-advisory-family not reached A tracked product family named in Oracle's own risk matrix. CPE cannot carry a suite name, only a module.

14 cna-named-product not reached A tracked product named in words by the CVE's own CNA, on a record with no CPE yet. Apache and Eclipse publish these on advisory day, before NVD adds CPE data.

15 non-deployable-product not reached The only affected product being a sealed appliance image, where Java runs but no -javaagent can be attached

16 unmatched-product not reached No tracked product matched above, and none present at all

disposition: What do we do about one that is? every rule runs

17 patch-hint decided it matched Mitigation candidate References include candidate fix URL (commit tier): https://github.com/yamcs/yamcs/commit/4d47d5cdcf5d92c2c5bbbc19feada422923332e3

18 open-source-maven skipped The affected package being open source on Maven, so the fix can be read

19 poc-derivable skipped An indexed exploit clearing the evidence bar to reverse-engineer, where there is no source to read

20 no-exploit skipped Nothing to build a rule from yet: no published exploit, no CISA record of exploitation and no source-level change to read

21 secure-rule-match no match A vulnerability class already blocked by an ARMR security rule

22 exploited-no-fix-or-poc skipped Somebody exploiting this CVE (a CISA or VulnCheck KEV listing, or a CISA verdict of active exploitation), with no fix, source code or PoC to build a rule from

23 below-action-threshold withheld Has 1 known POC(s) clearing the evidence bar — requires review despite MEDIUM severity

24 no-exploit-published no match A CISA or VulnCheck KEV listing, a CISA verdict of active exploitation, a reviewed exploit catalogue, or a GitHub PoC with 5 or more stars carries this CVE — exploit code is in use or published, so it stays a candidate

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