Medium Access control

CVE-2026-72724 — Discourse: Private Chat Threat Message Disclosure via Chat Onebox Channel/Threat ID Mismatch

Discourse is an open-source discussion platform. Prior to 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0, plugins/chat/lib/chat/onebox_handler.rb resolves Chat::Thread by route thread_id independently of the route channel_id before checking whether the user can preview the selected chat channel. An authenticated user can pair a public channel ID with a private thread ID in a /onebox.json request and obtain private thread message content. This issue is fixed in versions 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0.

Published Aug 10, 2026 · Updated Oct 15, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: GitHub_M

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

Technical severity (medium)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

—

No EPSS score.

Affects

Discourse

CVSS base

4.3

Medium · 2 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation

None

none · proof-of-concept · active

Automatable

can an attacker script the kill-chain steps

Technical impact

Partial

partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Discourse Discourse).
No fix documented in the sources: reduce exposure and monitor the vendor advisory.
Search available logs for exploit probes matching the vulnerability class (access control), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Discourse	Discourse	version < 2026.1.6version >= 2026.5.0-latest, < 2026.5.2version >= 2026.6.0-latest, < 2026.6.1version >= 2026.7.0-latest, < 2026.7.0	Vulnerable	CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Network

Attack complexity

Low

Privileges required

Low

User interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

None

Availability

None

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
4.3	CVSS 3.1	Medium	2.8	1.4	security-advisories@github.com via NIST National Vulnerability Database
4.3	CVSS 3.1	Medium	—	—	GitHub_M via CVE Program (cve.org) e CISA ADP

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N (score shown at the top: security-advisories@github.com)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-639 · Authorization Bypass Through User-Controlled Key (IDOR)

Other CVEs with this weakness →

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
Audit administrative actions and access to resources outside each user’s normal pattern.

web/proxy/WAF logsnetwork IDS/IPSauthentication logsapplication logs

Timeline

What happened to this CVE, newest first.

2026
Affected products added · discourse/discourse
Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
SSVC assessment updated
Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 15, 2026
CVSS changed · 4.3
Oct 15, 2026 · NIST National Vulnerability Database
Source status changed · → Deferred
Oct 15, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 15, 2026 · NIST National Vulnerability Database
CVE published
Aug 10, 2026 · GitHub_M

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 15, 2026 – Oct 15, 2026

References

9 on the record

github.com/discourse/discourse/security/advisories/GHSA-8g98-fvfc-9w48
x_refsource_CONFIRM, NIST National Vulnerability Database
github.com/discourse/discourse/pull/42092
x_refsource_MISC, NIST National Vulnerability Database
github.com/discourse/discourse/commit/dc54846f0754799591717b6018343e49524e41ce
x_refsource_MISC, NIST National Vulnerability Database
github.com/discourse/discourse/pull/42094
x_refsource_MISC, NIST National Vulnerability Database
github.com/discourse/discourse/commit/1276d7032af8803956c74ae87ccfd976938dcd75
x_refsource_MISC, NIST National Vulnerability Database
github.com/discourse/discourse/commit/49efe1d7f098f2ce7301908815a211cc9248270f
x_refsource_MISC, NIST National Vulnerability Database
github.com/discourse/discourse/commit/45ab6d54076de9ca4965888974d4416d5b48e83c
x_refsource_MISC, NIST National Vulnerability Database
github.com/discourse/discourse/pull/42093
x_refsource_MISC, NIST National Vulnerability Database
github.com/discourse/discourse/pull/42091
x_refsource_MISC, NIST National Vulnerability Database

Elsewhere on this site

Discourse
every CVE for this vendor

Access control
same class

CWE-639
other pages naming this weakness

Related CVEs (same products)

High CVE-2026-91159 Discourse: Stored oEmbed HTML injection via allowed iframe 1d
High CVE-2026-91157 Discourse: Media uploads remain publicly accessible after category permissions are restricted 1d
High CVE-2026-91156 Discourse: Chat MessageBus delivers read-restricted messages to unauthorized users 1d
Medium CVE-2026-59829 Discourse: Review queue exposes flag-related private message excerpts to category group moderators Aug 17, 2026
Medium CVE-2026-55704 Discourse: Shared-draft titles and excerpts leak through group post serialization Aug 17, 2026
Critical CVE-2026-55674 Discourse: Cache poisoning/XSS via color scheme cookies Aug 17, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No FIRST EPSS score.
No fixed version, patch or mitigation documented.
No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-72724 is "Discourse: Private Chat Threat Message Disclosure via Chat Onebox Channel/Threat ID Mismatch", rated Medium. It affects Discourse (Discourse); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 4.3 describes technical severity. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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