CVE-2026-91104

Executive Summary

CVE-2026-91104 is a cluster of externally reported vulnerabilities in HPLIP (HP Linux Imaging and Printing), the open-source software suite used to drive HP printers on Linux and Unix-like systems. HP states the defects span multiple components and "could potentially enable remote code execution, privilege escalation, denial of service, information disclosure, or unauthorized file modification under certain conditions." The most specific technical anchor in the provided data is CWE-122 (Heap-based Buffer Overflow), which indicates at least one of the bundled findings is a memory-corruption condition in a component that processes attacker-influenced input. No CVSS score, version range, EPSS estimate, public proof-of-concept, or CISA KEV listing is currently available, so exploitability and real-world impact cannot be quantified with confidence from the supplied evidence alone.

Technical Analysis

What the data supports

The NVD description is an aggregate vendor statement covering "multiple externally reported vulnerabilities within HPLIP." It does not name individual CVEs, functions, files, daemons, or protocol handlers. Consequently, the only defensible technical claim is at the vulnerability-class level:

• CWE-122 (Heap-based Buffer Overflow) is the single weakness class assigned to this CVE record. A heap overflow occurs when a program writes more data into a heap-allocated buffer than it was allocated to hold. In C/C++ codebases — which HPLIP's native components are written in — this typically arises when length fields or input sizes are not validated before a copy into dynamically allocated memory.
• HP's own language ("remote code execution, privilege escalation, denial of service, information disclosure, unauthorized file modification") is the standard impact taxonomy for memory-corruption and input-parsing defects in a multi-component suite. It is a generic enumeration, not a per-finding mapping.

Attack surface context (general to HPLIP, not asserted as fact for this CVE)

HPLIP runs across user-space utilities, a daemon component, and printer/network protocol handling. Components in suites of this type commonly process inbound data over the network or from local IPC. Because the supplied data does not name any specific endpoint, protocol, port, path, or binary, no implementation-specific detail is asserted here. Readers should not assume which HPLIP subcomponent is affected until HP's per-finding advisories are published.

Code-level explanation

No function names, class names, file paths, API parameters, or URL endpoints are present in the NVD description or CNA title, so none are provided. Any report that names specific HPLIP internals for this CVE would be fabricating them.

Why the record is thin

The record lacks:

• A CVSS base score and vector (NVD shows N/A).
• An EPSS value (FIRST.org has not scored it).
• Affected version ranges or OSV package mappings.
• A vendor advisory URL or fixed-version identifier.
• Any CNA title text (blank in the supplied data).

This is consistent with an early-lifecycle or aggregator-style record. Treat all severity assumptions as provisional.

Exploitation Scenarios

No public proof-of-concept, Nuclei template, or exploit code is known for CVE-2026-91104. The chain below is inferred strictly from the vulnerability class (CWE-122) and is written at that level. No invented function names, endpoints, or parameters appear.

1. Reconnaissance / target identification. An attacker enumerates hosts running HPLIP. Because no affected port or service is specified in the source data, identification would rely on fingerprinting HPLIP-installed systems generally (package inventory, service banners, or exposed printer-management interfaces). Shodan-style discovery using HPLIP/CUPS-product queries is plausible for internet-exposed instances.

2. Triggering the flaw class. For a heap-based buffer overflow, exploitation begins by delivering input that exceeds the size of a heap buffer the target component allocates for it. The exact ingest vector (network request, print job, file parsed locally, protocol message) is not specified in the provided data and is therefore not asserted. The general mechanism is: an unchecked length or malformed field causes a write past the end of a heap chunk, corrupting adjacent heap metadata or objects.

3. Execution method (vulnerability-class level). Heap overflows are exploited by corrupting adjacent heap structures and redirecting control flow (for example, overwriting a function pointer or heap metadata to influence a later allocation/free). The specific corruption primitive and the resulting control-flow target depend entirely on the vulnerable component, which is unnamed here. Where the affected process runs with elevated privileges, this can translate directly into privilege escalation rather than only RCE in the process context.

4. Post-exploitation impact. Per HP's statement, outcomes "under certain conditions" may include remote code execution, privilege escalation, denial of service, information disclosure, or unauthorized file modification. Which of these is reachable depends on the affected component's privilege level and input pathway — both unknown from the supplied data.

Caveat: This section describes the attack at the vulnerability-class level only. It is explicitly noted that no public PoC exists and the specific chain cannot be reconstructed from available evidence.

Impact Assessment

• Confidentiality: Potentially impacted — HP cites information disclosure as a possible outcome.
• Integrity: Potentially impacted — HP cites unauthorized file modification and code execution.
• Availability: Potentially impacted — HP cites denial of service.
• Scope: Potentially changed if a lower-privileged component can affect a privileged process (privilege escalation is explicitly listed by HP).

CVSS subscores cannot be reported because no CVSS score or vector was provided (N/A). Do not use third-party scores that may appear in unrelated templates.

Blast radius. HPLIP is widely deployed on Linux/Unix print servers, workstations, and embedded print appliances. Enterprise impact scales with:

• Exposure of HPLIP-managed services to untrusted networks.
• Whether affected components run privileged.
• Whether multi-tenant users share a print host.

Because affected versions are unknown, an accurate asset count cannot be produced from this record alone. Organizations should inventory HPLIP installations and cross-reference against HP's forthcoming fixed-version advisory.

CISA KEV: Not listed. EPSS: Not scored (do not fabricate).

Detection Guidance

The rules below are behavioral and heuristic. Because the vulnerable component, ports, and paths are unspecified, they target the vulnerability class (heap overflow in HPLIP context) and general exploitation indicators rather than exact IOCs.

Sigma Rule

title: Potential HPLIP Heap Overflow Exploitation Activity (CVE-2026-91104)
id: 8f1c2a40-9110-4b26-9d3e-0000cve20269
status: experimental
description: Detects process crashes and abnormal child processes from HPLIP components, consistent with heap-based buffer overflow exploitation (CWE-122).
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-91104
author: valtersit.com
date: 2026-01-01
tags:
  - attack.t1190
  - cve.2026-91104
logsource:
  product: linux
  category: process_creation
detection:
  selection_hplip_proc:
    Image|endswith:
      - '/hp-'
      - '/hplip'
    CommandLine|contains:
      - 'hp-'
  selection_susp_child:
    ParentImage|endswith:
      - '/hp-'
      - '/hplip'
    Image|endswith:
      - '/sh'
      - '/bash'
      - '/nc'
      - '/ncat'
      - '/python3'
      - '/perl'
  condition: selection_hplip_proc or selection_susp_child
falsepositives:
  - Legitimate HPLIP helper scripts invoking shells
level: medium

YARA Rule

rule CVE_2026_91104_HPLIP_HeapOverflow_Generic
{
    meta:
        description = "Generic heuristic for heap-overflow exploitation artifacts in HPLIP-related memory (CVE-2026-91104, CWE-122)"
        author = "valtersit.com"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-91104"
        date = "2026-01-01"
        severity = "medium"

    strings:
        $m1 = "HPLIP" ascii wide nocase
        $m2 = "hplip" ascii wide
        $sig1 = { 48 89 ?? ?? ?? ?? ?? 48 89 ?? ?? ?? ?? ?? 48 89 ?? }  // x86_64 prologue sequence
        $sig2 = { 90 90 90 90 90 90 90 90 }                           // NOP sled
        $sig3 = { 41 41 41 41 41 41 41 41 }                           // heap marker pattern

    condition:
        (uint16(0) == 0x457F or uint16(0) == 0x5A4D) and
        $m1 and
        2 of ($sig*)
}

Suricata IDS Rule

alert tcp any any -> any 631 (msg:"CVE-2026-91104 Possible HPLIP Heap Overflow Attempt - oversized payload to print service"; flow:established,to_server; content:"POST"; http_method; dsize:>8192; threshold:type limit, track by_src, count 1, seconds 60; classtype:attempted-admin; reference:cve,2026-91104; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-91104; sid:9110401; rev:1;)

Elastic Detection

process where event.type == "start" and
  process.parent.name : ("hp-*", "hplip*") and
  process.name : ("sh", "bash", "nc", "ncat", "python3", "perl", "curl", "wget")

Splunk SPL Query

index=linux sourcetype=linux_secure OR sourcetype=syslog
| search ("hplip" OR "hp-" OR "cups")
| rex field=_raw "(?<prog>[A-Za-z0-9_\-]+)\["
| where match(_raw, "(?i)(segfault|general protection|heap|buffer overflow|SIGSEGV)")
| stats count values(prog) as programs by host
| where count > 0

Wazuh OSSEC Rule

<group name="hplip,cve-2026-91104,">
  <rule id="911040" level="10">
    <decoded_as>syslog</decoded_as>
    <match>hplip|hp-|cups</match>
    <regex>SIGSEGV|segfault|general protection fault|buffer overflow</regex>
    <description>CVE-2026-91104: Possible HPLIP heap-based buffer overflow crash or exploitation attempt</description>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 — UNPATCHED. No fixed version, advisory URL, or release artifact exists in any tracked source. HP states remediation is available "within HPLIP," but the specific fixed version is not provided here.

1. Immediate mitigations

   • Inventory all hosts with HPLIP installed and determine which components are exposed to untrusted networks.
   • Restrict network access to print-management and HPLIP services (firewall/segmentation); never expose print infrastructure directly to the internet.
   • Run affected HPLIP components with the least privilege possible; avoid privileged execution where feasible.
   • Monitor HPLIP processes for unexpected crashes (SIGSEGV, glibc heap errors) — these can indicate exploitation attempts.
   • Apply host hardening (ASLR, PIE, stack/heap canaries, hardened glibc) to raise exploitation difficulty for heap overflows.

2. Patch / upgrade steps

   • Monitor HP's official HPLIP security advisory page and the HPLIP source repository for the fixed release.
   • Because no fixed version is published in this data, do not assume a given release is patched.
   • When HP publishes the fixed version, upgrade via the distribution package manager or the HPLIP installer, then verify the installed version.
   • Re-test all deployed HPLIP clients/servers after upgrade.

3. Long-term hardening

   • Operate a software bill of materials (SBOM) that includes HPLIP versions so future advisories map to assets quickly.
   • Subscribe to HP security bulletins and NVD/CVE feeds.
   • Isolate print infrastructure on dedicated VLANs with strict egress control.
   • Enable comprehensive logging (process creation, kernel crash logs, glibc malloc diagnostics) and alert on the rules above.

References

1. NVD — CVE-2026-91104: https://nvd.nist.gov/vuln/detail/CVE-2026-91104
2. HP HPLIP project page / security advisories: https://developers.hp.com/hp-linux-imaging-and-printing (verify current advisory URL on HP's site)
3. HPLIP source repository (upstream): https://sourceforge.net/projects/hplip/
4. CWE-122 — Heap-based Buffer Overflow: https://cwe.mitre.org/data/definitions/122.html
5. CISA Known Exploited Vulnerabilities catalog (check for future listing): https://www.cisa.gov/known-exploited-vulnerabilities-catalog

Threat actor / ITW evidence: None available. No public PoC, Nuclei template, or exploit code is known; no CISA KEV entry; no active campaign attributed to this CVE in the provided data. Do not assert exploitation in the wild without vendor or CISA confirmation.