Temporal namespace write can shell the Worker Service host
Direct answer
Temporal namespace write can shell the Worker Service host, also tracked as CVE-2026-89139 / CVE-2026-87858 / Temporal Worker subprocess RCE is a high-severity threat campaign HOL Guard tracked from Sep 21, 2026 to Sep 21, 2026, verified against 9 primary sources and last reviewed Sep 22, 2026. Active tracking has ended and the record remains published as a permanent historical research record.
Temporal Server 1.31.0 before 1.31.3 includes a Worker Controller subprocess compute provider that can execute caller-supplied program and argv on the Worker Service host for an authenticated namespace writer. Sibling CVE-2026-87858 can retarget completion callbacks at the internal frontend as system administrator. Upgrade to 1.32.0, 1.31.3, or 1.30.7. On 1.30.7 and 1.31.3, after pre-fix servers have drained, also set callback.inspectSourceHeader=false; 1.32.0 ships it disabled.
Also tracked as CVE-2026-89139 · CVE-2026-87858 · Temporal Worker subprocess RCE · Temporal callback source header admin
- First observed
- Sep 21, 2026
- Last observed
- Sep 21, 2026
- Last reviewed
- Sep 22, 2026
- Tracking ended
- Sep 21, 2026
Record exports
Uncertainty and limitations
Read the evidence limits before acting on this record.
Both CVEs require authenticated namespace write. CVE-2026-87858 also needs an internal frontend with HTTP enabled and a non-empty callback allowlist. Confirm the exact image or chart tag against Temporal release notes.
- Authenticated namespace write is required for both CVEs; this is not unauthenticated internet RCE.
- CVE-2026-87858 requires internal frontend HTTP plus a non-empty callback allowlist; a stock empty allowlist denies external callbacks.
- Temporal Cloud is not affected by these self-hosted Temporal Server issues according to Temporal's Trust Center.
- For Temporal Server 1.30.7 and 1.31.3, callback.inspectSourceHeader=false is a required post-upgrade step after pre-fix servers have drained; 1.32.0 ships it disabled.
- Does not invent exploitation status; not on CISA KEV as of the reviewed source state.
Guard coverage and policy
What Guard's reviewed assertions do and do not claim for this campaign, and the reviewed starting points for defense.
No Guard coverage mapping or campaign-specific policy guidance is published for this record.
Safe next step. Campaign guidance is defensive context. It does not auto-apply policy or claim universal campaign coverage.
Timeline
Reviewed events, oldest first, each tied to a verified source.
- Disclosure
CVE-2026-89139 and sibling CVE-2026-87858 published for Temporal Server Worker subprocess RCE and admin callback retarget.
Sources:NVD CVE-2026-89139·NVD CVE-2026-87858
- Vendor action
Temporal documented fixed trains 1.30.7, 1.31.3, and 1.32.0. For 1.30.7 and 1.31.3, operators must also set callback.inspectSourceHeader=false after pre-fix servers have drained; 1.32.0 ships it disabled.
Sources:Temporal Server v1.31.3 release·Temporal Server v1.30.7 release·temporal PR 12021 auto-scaled-workers bump·temporal PR 11965 callback source header opt-in·Temporal Trust Center CVE announcement
- Update
HOL Guard published the operator blog covering CVE-2026-89139 clustered with CVE-2026-87858.
Source:HOL Guard operator write-up
- Correction
HOL reconciled the first-party Temporal remediation requirement for callback.inspectSourceHeader=false on 1.30.7 and 1.31.3.
Sources:Temporal Trust Center CVE announcement·HOL Guard operator write-up
Publication clock: 13.3 hours from reviewed disclosure timestamp to HOL publication; 24-hour high target; within target.
Reviewed artifacts
The specific artifacts this record concerns, as reviewed. Names and versions are shown as text; a registry link is not recorded here.
Temporal Server@>=1.31.0 <1.31.3genericpackageTemporal Server@>=1.30.0 <1.30.7genericpackage
Sources
Every claim on this record is traceable to the sources below.
- NVD CVE-2026-89139vulnerability database · observed September 21, 2026
- NVD CVE-2026-87858vulnerability database · observed September 21, 2026
- temporal PR 12021 auto-scaled-workers bumpmaintainer advisory · observed September 21, 2026
- temporal-auto-scaled-workers PR 129maintainer advisory · observed September 21, 2026
- temporal PR 11965 callback source header opt-inmaintainer advisory · observed September 21, 2026
- Temporal Server v1.31.3 releasemaintainer advisory · observed September 21, 2026
- Temporal Server v1.30.7 releasemaintainer advisory · observed September 21, 2026
- Temporal Trust Center CVE announcementvendor advisory · observed September 21, 2026
- HOL Guard operator write-upother primary · observed September 21, 2026
Campaign questions, answered
Temporal Server 0 before HOL Guard tracked the campaign from Sep 21, 2026 to Sep 21, 2026.
No. Active tracking ended Sep 21, 2026; this page remains as a labeled historical research record and does not imply the threat is currently active.
The record cites 9 primary sources, names 2 reviewed artifacts, and was last fully reviewed Sep 22, 2026 by HOL Guard Security Publishing. Its uncertainty and limitations are stated on the record itself.
Campaign guidance is defensive context. It does not auto-apply policy or claim universal campaign coverage.
The permalink above is permanent. The full record can be downloaded from this page as JSON, an artifact CSV, and a STIX 2.1 bundle, and corrections can be requested through the published correction path on the record. Both CVEs require authenticated namespace write. CVE-2026-87858 also needs an internal frontend with HTTP enabled and a non-empty callback allowlist. Confirm the exact image or chart tag against Temporal release notes.
Reviewed in full by HOL Guard Security Publishing.
- Published
- Last full review
- Last modified
Record HGTC-2026-49979A99