CVE-2026-21869Public exploitNetwork attack vector

Remote code execution via negative context discard

Published Jan 7, 2026 · Updated Jan 7, 2026

Out-of-bounds writes in ggml.ai llama.cpp commit 55d4206c8 and earlier allow remote attackers to crash the server or execute code. The completion parser copies a client-supplied negative n_discard into context-shift state, causing reversed KV-cache ranges and an out-of-range new_tokens index when the context fills. Network access to a llama-server instance with context shifting enabled is sufficient; authentication is not required, and the resulting memory corruption is deterministic.

CVSS severity8.8
High
EPSS probability0.52%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Out-of-bounds writes in ggml.ai llama.cpp commit 55d4206c8 and earlier allow remote attackers to crash the server or execute code. The completion parser copies a client-supplied negative n_discard into context-shift state, causing reversed KV-cache ranges and an out-of-range new_tokens index when the context fills. Network access to a llama-server instance with context shifting enabled is sufficient; authentication is not required, and the resulting memory corruption is deterministic.

The record

CVE
CVE-2026-21869
Published
Jan 7, 2026
Updated
Jan 7, 2026
Vendor
Georgi Gerganov
Product
llama.cpp
Classifications
CWE-787, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 7, 2026CVE publishedPublication date reported by the CVE source.
  2. Jan 7, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=<= 55d4206c8

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Georgi Gerganov · llama.cppversion=<= 55d4206c8

Published CVSS scores

8.8GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo