Thursday, October 8, 2026 · Week 41 Reading for Oct. 8 · Last entry Oct. 6
Paperclip Index
Paperclip IndexDocumented harm20Minor harm▼ 5 from a week ago · Oct. 8The Index

Hijacked by injectionPI-0039

Reprompt: a single click on a Copilot link let attackers keep steering a user's Copilot session

Varonis Threat Labs showed that instructions placed in the query parameter of a legitimate Microsoft Copilot link could take over the victim's Copilot Personal session after one click and keep it pulling and sending out personal data, even after the chat was closed. Copilot's leak protections applied only to the first request, so asking it to repeat each task bypassed them. Varonis reported it to Microsoft on Aug. 31, 2025; Microsoft had fixed it by the Jan. 14, 2026, disclosure, separately from its Patch Tuesday updates. Microsoft 365 Copilot for business was not affected.

Reported Jan. 14, 2026Happened in 2025Updated Oct. 6, 2026Rated under methodology v0.6

Control failure, trackedNot counted. No documented harm outside the developer, but the system broke a rule or crossed a limit. Tracked beside the index.
Harm
Harm: No harm reportedAdds nothing to the index.
Control
Control level 2, Instruction violationReported beside the index. It adds nothing to a harm reading; when no harm counts in a window, the highest eligible control level in the window is the reading.
Controlled testDeveloper confirmedInitiated by Outside attacker
Near miss

Near miss. Harm was plausible but prevented. It is rated only on what actually happened.

Not counted: no harm reportedEffect on the index

Sources

How we know

3 sources · developer confirmed. Links go to the original publishers; the summary above is in our own words.

  2. newsReprompt attack let hackers hijack Microsoft Copilot sessionsBleepingComputer · Jan. 14, 2026bleepingcomputer.com/news/security/reprompt-attack-let-hackers-hijack-microsoft…
  3. newsHow 'Reprompt' Attack Let Hackers Steal Data From Microsoft CopilotTechRepublic · Jan. 19, 2026techrepublic.com/article/news-reprompt-attack-microsoft-copilot

Why this rating

No harm reported; control failure level 2

Two separate assessments. Only documented harm can count toward the index.

Observed harm

No harm reported

Researcher demonstration on controlled accounts; no victims reported.

Not a finding that no harm occurred.

The harm scale
  1. 1 Negligible Inconvenience, easily remedied.
  2. 2 Minor Limited, recoverable harm.
  3. 3 Moderate Material harm needing significant effort to remedy.
  4. 4 Severe Severe harm to health, rights, property or essential services.
  5. 5 Catastrophic Society-scale harm or disruption beyond a community's capacity to cope.

Control assessment

Instruction violation

Copilot followed injected instructions and bypassed its own leak safeguard, but used only the user's own session access.

Reported beside the index. It adds nothing to a harm reading; when no harm counts in a window, the highest eligible control level in the window is the reading.

The control scale
  1. 1 Negligible Behaved as instructed. The problem was an ordinary error or a flawed output, with no rule broken.
  2. 2 Minor Broke an explicit instruction or rule, or gamed its goal, while staying inside its permissions and environment: for example, reward hacking, misreporting results, or following injected instructions within its permissions.
  3. 3 Moderate Acted outside the permissions it was given, deceived its overseers about its own actions, or tampered with oversight tools (logs, monitors, shutdown). Stopped by normal controls within an hour.
  4. 4 Severe Reached systems outside its permitted environment, or acquired money, compute or accounts without authorization. The type and mechanism say how.
  5. 5 Catastrophic The developer or operator lost control: the system copied its weights outside their control, replicated itself, or resisted being stopped for 24 hours or more.

Rating rationale

No external harm was reported from this controlled test. Control level 2 reflects following injected instructions within permissions and bypassing a safeguard without a permission breach.

The scales

Effect on the index

It does not count toward the Jan. 19 reading

The reading for the week to Jan. 19, 2026, with this record and without it. Harms count in full for two weeks after they are reported, then one level less every two weeks.

Not counted: no harm reported. 3 other records behind the reading for that week.

The arithmetic
The reading for the week of Jan. 19, recomputed
StepWith itWithout
Counts toward the index?documented, external, eligible evidenceNo—
Worst documented harm, ksets the band— (none counting)— (none counting)
Harms at that level, nposition in the band00
Highest control level breachedsets the reading only when no harm counts44
Readingrounded down4 Control failures only4 Control failures only
Inside the window of 4 weekly readings
Week toReadingBand
Jan. 19, 20264Control failures only
Jan. 26, 20264Control failures only
Feb. 2, 20262Control failures only
Feb. 9, 20266Negligible harm

Recalculated backcasts, not readings published at the time.

Revisions

What we changed

4 logged. Every change to a rating is logged here, with the reason.

  1. v4
    Oct. 6, 2026

    Ratings confirmed by the editor.

  2. v3
    Oct. 3, 2026

    Audit corrections. Event date moved from 2026-01 to 2025: Varonis disclosed the flaw to Microsoft on 31 Aug 2025, so the test predates that. The summary now says Microsoft fixed it by the 14 Jan 2026 disclosure, separately from Patch Tuesday (BleepingComputer's correction). Repaired the BleepingComputer URL, dated the sources (Varonis's page now shows only a June 2026 update date; TechRepublic's date is from the audit, as its page was not readable in the Oct 2026 check) and added a status note. Ratings unchanged.

  3. v2
    Sept. 30, 2026

    Rated: impact not reported; control type instruction violation.

  4. v1
    Sept. 30, 2026

    Backfilled from public reporting.

Cite and share

Use this record

Citation

Paperclip Index. “Reprompt: a single click on a Copilot link let attackers keep steering a user's Copilot session.” Record PI-0039. Reported Jan. 14, 2026; updated Oct. 6, 2026. Rated under methodology v0.6. https://paperclipindex.com/incident/PI-0039