CVE-2026-56755

Denial of Service (CPU & Memory Exhaustion) via O(N^2) String Concatenation in Debian Package Upload

Denial of Service (CPU & Memory Exhaustion) via O(N^2) String Concatenation in Debian Package Upload

Gitea's Debian package registry parser contains an unbounded decompression vulnerability in ParseControlFile. When processing an uploaded .deb file, the parser decompresses control.tar.gz and copies the entire uncompressed stream into a strings.Builder via a TeeReader, with no limit on how much data is read. Because DEFLATE compression can achieve ratios exceeding 100:1 on repetitive input, an attacker can craft an 83 MB .deb payload that expands to over 16 GB during parsing, exhausting server memory before any content validation runs. A second issue compounds this: continuation lines in the Description field are concatenated with += at modules/packages/debian/metadata.go:161 inside a loop, producing O(N²) allocation and copy work that stalls the CPU even at moderate line counts. Any authenticated user with write access to the package registry can trigger a complete denial of service with a single upload request to the handler at routers/api/packages/debian/debian.go:146.

Root Cause

There are two distinct root causes that can be exploited independently or together.

1. Unbounded decompression (decompression bomb) ParsePackage wraps the control.tar member in a decompressor but never constrains how many bytes that decompressor is allowed to produce:

https://github.com/go-gitea/gitea/blob/9155a81b9daf1d46b2380aa91271e623ac947c1e/modules/packages/debian/metadata.go#L88-L110

The resulting inner reader is passed directly to the tar reader, and from there to ParseControlFile. Inside ParseControlFile, every byte that the bufio.Scanner reads from the decompressed stream is simultaneously written into an unbounded strings.Builder via io.TeeReader:

https://github.com/go-gitea/gitea/blob/9155a81b9daf1d46b2380aa91271e623ac947c1e/modules/packages/debian/metadata.go#L147-L150

There is no call to io.LimitReader at any point in this chain. Other package format parsers in the same codebase — pub, conan, and cargo — all wrap their readers with io.LimitReader before consuming them. The Debian parser does not, making it the only one in the registry vulnerable to this class of attack.

2. O(N²) string concatenation For each continuation line belonging to the Description field, the parser appends to a plain string with +=:

https://github.com/go-gitea/gitea/blob/9155a81b9daf1d46b2380aa91271e623ac947c1e/modules/packages/debian/metadata.go#L158-L164

Because Go strings are immutable, every += allocates a new backing array and copies the entire accumulated description into it. A description with N continuation lines triggers O(N²) total bytes of allocation and copying. At 500 000 lines this produces roughly 250 GB of cumulative copy work, saturating a CPU core and driving the GC into a tight collection loop regardless of available RAM.

Reproducing

I have reproduced the issue in a Docker container with the following PoC. It may need tweaks based on the memory you are reproducing it with.

This has been reproduced on commit 9155a81b9daf1d46b2380aa91271e623ac947c1e.

All the files go in the gitea file directory.

cmd/poc/main.go

package main

import (
	"archive/tar"
	"bytes"
	"compress/gzip"
	"fmt"
	"io"
	"os"
	"runtime"
	"strings"
	"time"

	"github.com/blakesmith/ar"

	debian_module "gitea.dev/modules/packages/debian"
)

// targetUncompressed is the desired size of the uncompressed control file.
// Set comfortably above the 12 GB container limit so the OOM kill is reliable.
const targetUncompressed = 15 * 1024 * 1024 * 1024 // 15 GB

// padLine is the filler field written after the required package fields.
// Using…

Denial of Service (CPU & Memory Exhaustion) via O(N^2) String Concatenation in Debian Package Upload

Denial of Service (CPU & Memory Exhaustion) via O(N^2) String Concatenation in Debian Package Upload

Gitea's Debian package registry parser contains an unbounded decompression vulnerability in ParseControlFile. When processing an uploaded .deb file, the parser decompresses control.tar.gz and copies the entire uncompressed stream into a strings.Builder via a TeeReader, with no limit on how much data is read. Because DEFLATE compression can achieve ratios exceeding 100:1 on repetitive input, an attacker can craft an 83 MB .deb payload that expands to over 16 GB during parsing, exhausting server memory before any content validation runs. A second issue compounds this: continuation lines in the Description field are concatenated with += at modules/packages/debian/metadata.go:161 inside a loop, producing O(N²) allocation and copy work that stalls the CPU even at moderate line counts. Any authenticated user with write access to the package registry can trigger a complete denial of service with a single upload request to the handler at routers/api/packages/debian/debian.go:146.

Root Cause

There are two distinct root causes that can be exploited independently or together.

1. Unbounded decompression (decompression bomb) ParsePackage wraps the control.tar member in a decompressor but never constrains how many bytes that decompressor is allowed to produce:

https://github.com/go-gitea/gitea/blob/9155a81b9daf1d46b2380aa91271e623ac947c1e/modules/packages/debian/metadata.go#L88-L110

The resulting inner reader is passed directly to the tar reader, and from there to ParseControlFile. Inside ParseControlFile, every byte that the bufio.Scanner reads from the decompressed stream is simultaneously written into an unbounded strings.Builder via io.TeeReader:

https://github.com/go-gitea/gitea/blob/9155a81b9daf1d46b2380aa91271e623ac947c1e/modules/packages/debian/metadata.go#L147-L150

There is no call to io.LimitReader at any point in this chain. Other package format parsers in the same codebase — pub, conan, and cargo — all wrap their readers with io.LimitReader before consuming them. The Debian parser does not, making it the only one in the registry vulnerable to this class of attack.

2. O(N²) string concatenation For each continuation line belonging to the Description field, the parser appends to a plain string with +=:

https://github.com/go-gitea/gitea/blob/9155a81b9daf1d46b2380aa91271e623ac947c1e/modules/packages/debian/metadata.go#L158-L164

Because Go strings are immutable, every += allocates a new backing array and copies the entire accumulated description into it. A description with N continuation lines triggers O(N²) total bytes of allocation and copying. At 500 000 lines this produces roughly 250 GB of cumulative copy work, saturating a CPU core and driving the GC into a tight collection loop regardless of available RAM.

Reproducing

I have reproduced the issue in a Docker container with the following PoC. It may need tweaks based on the memory you are reproducing it with.

This has been reproduced on commit 9155a81b9daf1d46b2380aa91271e623ac947c1e.

All the files go in the gitea file directory.

cmd/poc/main.go

package main

import (
	"archive/tar"
	"bytes"
	"compress/gzip"
	"fmt"
	"io"
	"os"
	"runtime"
	"strings"
	"time"

	"github.com/blakesmith/ar"

	debian_module "gitea.dev/modules/packages/debian"
)

// targetUncompressed is the desired size of the uncompressed control file.
// Set comfortably above the 12 GB container limit so the OOM kill is reliable.
const targetUncompressed = 15 * 1024 * 1024 * 1024 // 15 GB

// padLine is the filler field written after the required package fields.
// Using…

Gitea: Denial of Service (CPU & Memory Exhaustion) via O(N^2) String Concatenation in Debian Package Upload in gitea.dev

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 *…