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Discourse CVE-2026-53961

| EUVDEUVD-2026-42728 MEDIUM
Insufficient Verification of Data Authenticity (CWE-345)
2026-07-09 security-advisories@github.com
Information Disclosure Discourse
6.5
CVSS 3.1 · Vendor: github
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Severity by source

Vendor (github) PRIMARY
6.5 MEDIUM
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
vuln.today AI
6.5 MEDIUM

Webhook is network-accessible with no Discourse authentication required (PR:N, AV:N); AWS account prerequisite is attacker-controlled, not a target-side access control (AC:L); impact confined to email revocation with no confidentiality loss (I:L, A:L, C:N).

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N

Primary rating from Vendor (github).

CVSS VectorVendor: github

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
Low

Lifecycle Timeline

2
Patch available
Jul 09, 2026 - 23:02 EUVD
Analysis Generated
Jul 09, 2026 - 22:44 vuln.today

DescriptionCVE.org

Discourse is an open-source discussion platform. Prior to 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5, the AWS SES bounce webhook at POST /webhooks/aws verified that SNS messages were signed by Amazon but did not bind them to trusted TopicArn values, allowing any AWS account holder to publish validly signed forged Bounce notifications that revoke a targeted user email. This issue is fixed in versions 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5.

AnalysisAI

Discourse's AWS SES bounce webhook endpoint (POST /webhooks/aws) validates Amazon SNS message signatures but omits TopicArn binding, allowing any AWS account holder to publish legitimately signed forged Bounce notifications that revoke a targeted Discourse user's email address. Versions prior to 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5 across all active release branches are affected when the SES integration is enabled. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Recon
Register or use existing AWS account
Delivery
Create attacker-controlled SNS topic
Exploit
Craft forged SES Bounce notification for target user email
Install
Publish via Amazon SNS (Amazon signs message)
C2
Submit signed payload to victim's POST /webhooks/aws
Execute
Discourse accepts valid signature without TopicArn check
Impact
Target user email address revoked
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Vulnerability AssessmentAI

Exploitation Exploitation requires that the target Discourse instance has the AWS SES bounce webhook integration enabled and the POST /webhooks/aws endpoint reachable over the network. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The NVD CVSS 6.5 with AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L accurately characterizes the attack surface: the webhook is internet-facing, no Discourse credentials are required, and no user interaction is needed. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker registers or uses an existing AWS account, creates an SNS topic, and constructs a valid SNS Bounce notification JSON payload targeting a known Discourse user's email address. Publishing this message through Amazon's SNS infrastructure causes Amazon to sign it with valid Amazon credentials; the attacker then delivers it to the victim Discourse instance's POST /webhooks/aws endpoint. …
Remediation Upgrade Discourse to 2026.6.0 (stable), 2026.5.1 (beta), 2026.4.2 (tests-passed), or 2026.1.5 (legacy), per the operator's active release branch. … Detailed patch versions, workarounds, and compensating controls in full report.
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CVE-2026-53961 vulnerability details – vuln.today
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