CVE-2026-78659VulnerabilityPublished 11 Oct 2026Updated 28 Oct 2026

Microsoft · HTTP/2 server memory exhaustion due to Trailer headers in net/http

Affects MicrosoftSource GCVE Database

Authoritative record:CVE-2026-78659· High 7.5

Not known to be exploited · CVSS 7.5 High · fixed in 1.26.9 : patch Microsoft soon.

Data as of 28 Oct 2026, 09:58 UTC

CVSS 3.1 base score

7.5High

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

Patch: Available – fixed in 1.26.9, 1.27.2, 0.60.0

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

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

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, 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: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 8 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: 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 26 Oct 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.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, 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.

microsoft-security-response-ce

What to do

Upgrade net/http to 1.26.9; net/http/internal/http2 to 1.27.2; golang.org/x/net/http2 to 0.60.0.

Affected software

Product	Affected	Fixed in
Go standard librarynet/http	Affected <1.26.9	Fixed in 1.26.9
Go standard librarynet/http/internal/http2	Affected >=1.27.0-0 <1.27.2	Fixed in 1.27.2
golang.org/x/netgolang.org/x/net/http2	Affected <0.60.0	Fixed in 0.60.0
Gonet/http`pkg:golang/net/http`Other threats	Affected <1.26.9	Fixed in 1.26.9
Gonet/http/internal/http2`pkg:golang/net/http/internal/http2`Other threats	Affected >=1.27.0-0 <1.27.2	Fixed in 1.27.2
Gogolang.org/x/net/http2`pkg:golang/golang.org/x/net/http2`Other threats	Affected <0.60.0	Fixed in 0.60.0

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

Description

CVE-2026-78659 is a vulnerability in Microsoft's HTTP/2 implementation (net/http) where Trailer headers can cause server memory exhaustion. This issue could lead to denial of service conditions by exhausting server resources. The vulnerability affects version 3.0 of the product. No CVSS score or detailed impact metrics are provided. No known exploits or patches are currently documented.

Impact

The primary impact is server memory exhaustion, which can degrade service availability or cause denial of service. No further impact details or exploitation reports are available.

Summary

This vulnerability involves the handling of Trailer headers in the HTTP/2 server implementation within Microsoft's net/http component. Improper processing of these headers can lead to memory exhaustion on the server, potentially causing denial of service. The affected version is 3.0. There is no public information on exploit code or active exploitation.

CWE-405Asymmetric Resource Consumption (Amplification) (opens in a new tab)
Class weakness
The product does not properly control situations in which an adversary can cause the product to consume or produce excessive resources without requiring the adversary to invest equivalent work or otherwise prove authorization, i.e., the adversary's influence is "asymmetric."
Architecture and Design
An application must make resources available to a client commensurate with the client's access level.
Architecture and Design
An application must, at all times, keep track of allocated resources and meter their usage appropriately.
System Configuration
Consider disabling resource-intensive algorithms on the server side, such as Diffie-Hellman key exchange.
OWASP Cheat Sheets
File Upload (opens in a new tab)
OWASP ASVS 4.0.3
V12.1.1 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 28 Oct 2026, 09:58 UTC

WeaknessesCWE-405

Technical details

References

Community reviews

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