CVE-2026-117556VulnerabilityPublished 27 Oct 2026Updated 3 Nov 2026

Red Hat Security Advisory: Red Hat Hardened Images RPMs bug fix and enhancement update

Affects Red HatSource GCVE Database

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Authoritative record:CVE-2026-117556· Medium 5.3

Not known to be exploited · CVSS 5.3 Medium : upgrade Red Hat zchunk to 1.5.5 when convenient.

Data as of 3 Nov 2026, 07:30 UTC

CVSS 4.0 base score

5.3Medium

How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none

CVSS scores by source
CNA (VulnCheck)	CVSS 4.0	5.3
CNA (VulnCheck)	CVSS 3.1	4.3

Patch: Available – fixed in 1.5.5

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: Passive
Vulnerable system confidentiality: None
Vulnerable system integrity: None
Vulnerable system availability: Low
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: Passive: Successful exploitation of this vulnerability requires limited interaction by the targeted user with the vulnerable system and the attacker’s payload. These interactions would be considered involuntary and do not require that the user actively subvert protections built into the vulnerable system.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the Vulnerable System are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 27 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade zchunk and zchunk/zchunk to 1.5.5.

Affected software

Product	Affected	Fixed in
zchunkzchunk	Affected <1.5.5	Fixed in 1.5.5
GitHubzchunk/zchunk`pkg:github/zchunk/zchunk`Other threats	Affected <1.5.5	Fixed in 1.5.5

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Red Hat has released updated zchunk packages (version 1.5.5-1.hum1) containing the fix for this vulnerability. Users should apply these updates to remediate the issue. No other mitigations are recommended or available. Because the vulnerability requires processing untrusted files, exposure is limited in typical Red Hat use cases.

Description

CVE-2026-117556 is a low severity vulnerability in the zchunk component used in Red Hat Hardened Images RPMs. It involves improper boundary checking during file header parsing, which can cause an out-of-bounds read and lead to a denial of service (application crash) when processing a specially crafted file. Exploitation requires handling an untrusted file, which is unlikely in typical Red Hat environments where zchunk operates on trusted, cryptographically verified repositories. The vulnerability does not allow system compromise or unauthorized access.

Impact

The vulnerability causes an application crash (denial of service) when processing a malformed file header in zchunk. There is no impact on confidentiality or integrity, and no escalation to system compromise or unauthorized access is possible. The risk is minimal in Red Hat environments due to the trusted nature of package metadata sources.

Summary

A flaw in zchunk allows a remote attacker to cause a denial of service by triggering an out-of-bounds read during file header parsing. This occurs due to improper boundary checking, leading the program to read beyond allocated memory and crash. The vulnerability is rated low severity because exploitation requires processing a malicious file, which is limited in Red Hat environments where zchunk is used with trusted package metadata. The impact is limited to transient user-space execution termination without further system compromise. Red Hat has released updated zchunk RPMs (version 1.5.5-1.hum1) for multiple architectures to address this issue.

CWE-125Out-of-bounds Read (opens in a new tab)
Base weaknessCWE Top 25 (2025): #8
The product reads data past the end, or before the beginning, of the intended buffer.
Implementation · Input Validation
Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
Architecture and Design · Language Selection
Use a language that provides appropriate memory abstractions.
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
V5.1.3 (opens in a new tab)
Attack patterns
Overread Buffers (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 3 Nov 2026, 07:30 UTC

WeaknessesCWE-125

Technical details

References

Community reviews

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