Cross-namespace privilege escalation via trusted callback header
Published Sep 21, 2026 · Updated Sep 21, 2026
Privilege escalation in Temporal Server allows remote authenticated users to perform administrative operations across namespaces. The HSM and CHASM callback routers trust a caller-supplied source header, rewrite only the scheme and host, and preserve an attacker-chosen API path and body. Exploitation requires namespace write access, authorization, an allowed callback host, and an internal frontend HTTP port; successful requests can alter or delete other namespaces and workflows.
Summary
What happened
Privilege escalation in Temporal Server allows remote authenticated users to perform administrative operations across namespaces. The HSM and CHASM callback routers trust a caller-supplied source header, rewrite only the scheme and host, and preserve an attacker-chosen API path and body. Exploitation requires namespace write access, authorization, an allowed callback host, and an internal frontend HTTP port; successful requests can alter or delete other namespaces and workflows.
The record
- CVE
- CVE-2026-87858
- Published
- Sep 21, 2026
- Updated
- Sep 21, 2026
- Vendor
- Temporal Technologies
- Product
- Temporal Server
- Classifications
- CWE-807, T1068
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Sep 21, 2026CVE publishedPublication date reported by the CVE source.
- Sep 21, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=1.25.0 <=1.29.7
- Affected versionversion=1.30.0 <1.30.7
- Affected versionversion=1.31.0 <1.31.3
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Activity data is delayed. The latest report is Sep 28, 2026.
Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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